Gum snapping. There is a lady who sits across the aisle from me who loves to snap her gum, she does it with mouth open and snaps it through her teeth. She's a nice lady and all, but it drives me crazy, every couple of seconds, 'CRACKLE, SNAP!'
I've said things like, 'What was that? Is that you?' and she just laughs and says, 'Yeah.' I don't think she even realizes she does it evertime she has gum, which is almost daily. I guess I need to burn some MP3's on dvd and listen to them to drown her out.