"Estar rayado(a)" = To be scratched*

Go crazy. To go on over and over again about the same isuue/ problem as if you were listeling to a scratched disc in your head. The verb "rayarse" implies inner stress and it shares synonym expressions such as "darle demasiadas vueltas a las cosas", "comerse la cabeza". However, you can also "rayar a alguien" by bothering and nagging until you become a pain.
"Desde que no tengo noticas suyas estoy muy rayado/a y no paro de comerme la cabeza"
"No me rayes más por favor. Bastantes vueltas le he dado ya al asunto"
"¡Déjalo ya! Me estás rayando"

"Aguafiestas" = Waterparties*

Wet blanket or kill-joy always spoiling the good news or plans.

"Hacer piña"= To do pinecone*

To stick together as a group in order to offer mutual support and be stronger. Cooperation among people, i.e. "Trabajar todos a una"
"Cuando se trabaja en equipo es fundamental hacer piña para tener buenos resultados"
"El equipo ganó porque hicieron piña desde el primer momento"

"Perder los papeles" = To lose the papers*

To lose your nerves "Perder los nervios" and to act in an irrational way.

"Poner verde a alguien"= To put someone green*

To criticise people behind their back. Another colloquial expression with the same meaning is "poner a parir" (to put to give birth*) or even "poner a caer de un burro"
Cuando se fué, lo pusieron verde todos.
No entiendo por qué a Juan le gusta poner verde a sus compañeros.
Nuria puso a parir a los suegros = Nuria puso a sus suegros a caer de un burro.

Please! Do not confuse with the expression "Estar verde" (To be green*) which means to be young and unexperienced as well as not knowledgeable in a subject.

"Ser un(a) perla" = To be a pearl*

Ironic expression to refer to someone who usually misbehaves. The expression "Ser un caso" carries a similar meaning and if the behaviour is extreme in a bad way, people say "Ser un caso perdido"(to be a lost case*)
 "Tiene un niño que es un perla"
"Cuidado con ella, que es una buena perla" 
"Los alumnos de ese grupo son un caso (perdido)".

"Liarla parda" = To roll it dun*

To get yourself into trouble. Mess something up. People usually use "La he liado parda" (fixed expression) when they want to confess they have done something wrong and are in trouble.

"Hacer la pelota"= To do the ball*

To butter someone up. It's usually "done" to parents, teachers and bosses, but you can "hacer la pelota" to whomever you want.
"No es por hacer la pelota, pero la comida estaba buenísima"
"Mi hermano le hace la pelota a mis padres antes de pedirles un favor"

"Ser un callo" = To be a callus*

To be extremely ugly. As I once read: to have a face like the back of a bus! :/
Guess what! You can make it even more authentic by giving it a particular nationality ->  "Ser un cayo malayo" = To be a malaysian callus*           
(My apologies to all my malaysian friends! No ofence intended).

"Hacer picón" = To do charcoal*

Both "hacer picón" or "hacer tabaco" are expressions typically used in the passive to say that something has been destroyed, torn to pieces. The image is so plastic that it can be used to refer to a person being tired.
La tele está hecha picón / tabaco.
No voy a salir, estoy hecho picón / tabaco.

"Hacer el indio"= To do the indian*

People can use it with the plain meaning of doing silly things, but it normally carries a special nuance of doing stupid things that lead to embarrass yourself.  You can go for the typical "hacer el ridículo", but you want to do better than that, huh? ;)
Use this expression unchanged, irrrespective of your gender.

"Ser el útlimo mono" = To be the last monkey*

When you use that idiom (the same form for male and female) you are complaining from being ignored or being always left behind. Yes, when you are the last monkey, you are kind of the weakest link, goodbye!

"Marear la perdiz"= To make the partridge dizzy*

To beat around the bush i.e. avoiding to get to the point intentionally!

"Quedarse a cuadros" = Stay checked*

Unable to react as a result of shocking or unexpected news.

"Poner lo dientes largos a alguien"= To put someone's teeth long*

To make someone green with envy. Basically, you show off about something you have and make others want it too.

"Poner Ojitos" = To put little eyes*

Although this expression is mainly used for flirting looks, you can also "put little eyes" to get what you want! If there is an expert in "poner ojitos" that is certainly Puss in Boots ;)

  

"Bailar el Agua"= To dance the water*

Adulate and flatter to humour someone.
"Seguir la corriente" (to follow the current) meaning "to play along" is a similar expression. A more informal way to go for this meaning would be "decir que sí como a los locos" (to say yes as you would to a crazy person)

"Estar empanado(a)"= To be breaded*

To be extremely absent-minded or not paying atention. A less familiar way of saying it is "Estar en la luna" (to be on the moon)
¡Éste siempre está empanado y nunca se entera de nada!

"Comer la oreja" = To eat the ear*

Something as simple as to try and persuade somebody by insistently talking to him/her.
A more negative nuance is conveyed in alternative expressions such as "comer la olla" (eat the pan) and "comer el tarro" (eat the jar) in the sense that the person is doing your head in.

"Quedarse pajarito" = Remain little bird*

To freeze to death.
Other expressions with "pajarito" are shared in both languages as the examples show: "Un pajarito me ha dicho..." (A little bird told me....) and "Comer como un pajarito" (Eat like a bird)

"Ir hecho un pincel" = To go made a paintbrush*

Definitely, a translation on this one is more than welcome to make sense out of the literal meaning. This funny expression refers to the fact that the person is elegantly and neatly dressed. The opposite, i.e. to be informally dressed or with ordinary clothes would be "ir de trapillo" to go of little cloth*

"Montar un pollo" = ride a chicken*

I know! It is difficult to belive that this sentence means to make a scene but it is definitely used. So, whenever you are mad at someone for some wrong done to you, you are allowed to ride a chicken ;)
For a change, you can say "montar un numerito" (ride a little number), also commonly used with the same meaning.

"Dar la lata"= Give the can / tin*

There are many ways to express that someone or something is nagging you. Here is a short list: Dar la lata = to give the can / tin, Dar la vara= to give the rod, Dar la murga= to give the street band, Dar la tabarra= to give the badgering, Dar el coñazo(fam!) = to be a real pain (only use this expression with people you are familiar with)

"Ser un huevón(a)" = To be a big egg*

More "eggy" expressions ;) If you are told to be a "huevón" o "huevona" is because you are a very laid-back, slow and even lazy. Sometimes, the expression gets "harder" and you can be called "huevo duro" (hard-boiled egg). That is a step beyond in describing you, as you have been promoted to the status of "thick".

"En abril, aguas mil"= In April, thousand waters*

This is a proverb which points to the fact that rain is expected in this month. What is more, winter is not really over until April is gone. May is the first really warm month. An English saying confirms this same theory: "April showers bring May flowers".

"Cantar las Cuarenta" = To sing the forty*

That is definitely done when we want to tell someone a few home truths.