A: What time is it?
B: Eleven straight up.
A: OK, thanks bud.
I'm sitting at my workstation looking for my cell phone to check the time and wondering if I've ever heard this expression before. So it's eleven o'clock... Well a new phrase for me.
I don't think I had ever paid attention to the time being expressed this way. I can assure you that on the many books I used to learn/teach English (as a second/foreign language), this was never taught as an option for telling time. I right away wrote it on a post-it so I would remember it.
I got home and told my husband that I had heard a new phrase. Of course he knew it, but he knows I get excited to discover and learn new idiomatic expressions. So if the minute hand on a clock is "straight up" at twelve, instead of saying it is (number) o'clock, you could say it is (number) straight up. Now I just need to find a good situation to use it and put it in practice.