I am a people watcher. I could spend hours sitting on a bench in front of a well populated, character filled environment. Today, on a beach a man with his diaper-only clad three year-old daughter sat feet behind me. I'd been enjoying the fun filled, crowded beach for two hours when he showed up with a hacking cough and a cell phone. His kid was running around and he was on his cell shouting about paying a woman $2,300 for "nothing". He'd sold his house and was cleaning out the garage ... yes, I know too much.
You can find personalities for your characters anywhere! When I want an annoying habit for a sub-character I will pull on my experience from today and there you have it ... an inconsiderate loud talker, a germ-infesting spitter or a disconnected dad.
Sometimes I would never be able to use some of the people I watch ... they are too over the top and unbelievable. I love those people!
I don't keep a notebook to write this stuff down - used to, but never cracked it open again. My advice, try keeping notes and see how it goes.