Learn English with idioms

An idiom is an expression in the usage of a language that is peculiar to itself either grammatically (as no, it wasn't me) or in having a meaning that cannot be derived from the conjoined meanings of its elements (as ride herd on for “supervise”).
In class (1ª ESO, 2ºESO) we learnt very interesting idioms with this video:

A face like thunder : cara de pocos amigos
Packed like sardines: como sardinas en lata
A skeleton in everyone's closet: tener secretos de familia
It's raining cats and dogs: llueve a cántaros
Don't look a gift horse on the mouth: a caballo regalado no le mires el diente
When in Rome, do as Romans do: donde fueres, haz lo que vieres
Make my day: alegrarte el día
As cool as a cucumber: fresco como una lechuga
Sick as a parrot: sentirse fatal