This expression is utterly common and should be used every time the appropriate circumstances appear. Pérate (PE•dah•teh) is a shorter version of espérate, which is an imperative meaning 'wait' or 'stop it' depending on the context. Pérate usually comes in two forms.
Pérate-pérate is used to express confusion or lack of clarity in someone's ideas or speech. It is usually followed by barajéamela más despacio, which literally means 'deals the cards more slowly' and implies a request for a slower, simpler explanation.
¡Pérateeeee! is used when somebody is being bugged physically or verbally--typically a friend or a family member. It shows the subject is irritated and the next reaction might be physical aggression.
Lupita: Licenciado, acaban de llamar, que la grúa se lo llevó, y que el corralón está cerrado por el puente, y...
Lic. Fuentes: Pérate-pérate Lupita. Respira primero. Ahora sí. ¿Qué chingados le pasó a mi nave?
Lupita: Sir, they just called, the towcar towed it, it's in the pound, and it's closed because of the long weekend, and...
Mr. Fuentes: Wait, wait, Lupita. Breath first. Now, what the fuck happened to my ride?
Compañerito: Mochilas con los Pulparindos, no seas gacho, ándale, ándale... ándale
Pepito: ¡Pérateeee!... ¡Qué bien chingas! Si tus jefes no te dan camarón, ponte buzo con los cambios.
Classmate: Share your candies, don't be rude. C'mon... do it, c'mon.
Pepito: Drop it... Stop bothering! If your parents don't give you money you've gotta be smart and keep the change when you do chores for them.