A side-piece is a gal that may or may not think she’s your main girlfriend, but she most definitely is not.
I was in Brooklyn Friday night. That means that I wasn’t in, say.. Zimbabwe, Africa.
If someone hires Gloria Allred to say “Bill Cammack was in Zimbabwe Friday night! :O”, I’ll probably ignore it completely.
If I elect to speak on it, I’m going to say “No.. In fact, I was not in Zimbabwe Friday night.”, and that’s going to be the end of it.