Here is one that sometimes baffles those learning English..."Go and catch that bus!" You wouldn't think this was an colloquial expression. Think about it from a non-English speaker's viewpoint. What do you mean go "catch" (literally?!?) the bus? If I tried that, I would be killed! Of course, it really means go and wait for the bus and when it arrives...board it. Normally, we native English speakers don't ever think about it. We have more idioms than we realize simply because it is woven into our culture and way of life. The same is true in other languages.
The hallmark of a non-native's mastery of any language is when they understand many colloquial expressions...not just the standard constructs.
Hear are some that I either heard of or have said myself.
1) Shooting the breeze (two people yapping)
2) If it is Tuesday, it must Belgium (comes from a movie and it refers to traveling)
3) You can't eat your cake and have it too! (Everybody seems to think they can...go figure)
4) Hot air convention (usually refers to business meetings)
5) Going the whole nine yards (nobody is sure what this refers to but the gist of the expression makes sense)
6) So, you gored my ox (not literally of course)
7) I'm having a bad hair day (most people should know this one)

8) Are you flatlining on me again? (refers to a ridiculous statement somebody made)
9) Thanks, I really needed that (not! - said in irony)
10) Are you making mountain out of a molehill or anthill (whichever you prefer)
11) I'm hearing the wind (a statement directed to somebody doing an airhead routine on you and you can "hear" the wind through their ears)
12) Ah, I see you lowered your wind resistance (a reference to somebody who got a haircut - typically male directed) I made that one up years ago and tried it on a former co-worker and once he figured it out...he just laughed and laughed and said he loved that one.
13) Pay me now or pay me later (remember that Fram Oil Filter commercial?)
14) Was I born yesterday? (Do I look that stupid to you?)
Oh...that was fun and got me thinking of more...