I'm from Mexico though I've spent most of my time in the United States. Here are some idioms that I know.

Arroz con popote - lit. trans. - "rice with a straw". If you say someone eats/likes rice this way it implies that they are homosexual.

¿Se te hizo polvo? -"Did it turn into dust?" - You can ask someone this for example if they finished eating something fast because if it was dust it would blow away and be gone, which would explain why their plate is suddenly empty.

Sudé la gota gorda - "I sweated the fat drop" - Actually means that the person sweated a lot, usually because of some really hard work.

These are pretty lame in my opinion so here's a bonus one my mom told me:

Con un clavo sacas otro clavo - "With one nail take out another nail" - means that if you are upset about a failed romantic relationship, replace it with a new one.