Hi... in Venezuelan Spanish we have an expression that says:
"Aprieta ese rabo/culo/ esfinster/ orto" that means that you should be prepared for a really bad time to come...
For example here some Venezuelans say:
"Aprieta ese culo que lo que viene es candela"... how would you translate it?
What I would say is: "You´d better get an ice-bag because we´re about to receive an ass-kick"
I saw transformers the other day and they made that translation, but I didnt hear the expression in English... so please hep