Whether it's the football team or the invoice, mostly to me the Bills mean money and time spent with a feeling of anticipation and excitement only to be disappointed when they come due.
I've had a number of friends who were Bills (the name, not actual Bills... I mean they were actually named Bill, but they weren't Buffalo Bills... I mean, I guess a few of them were since they lived in Buffalo, but they weren't on the team); better experience in general than the football team or the invoice type... except that one Bill. You know who you are, bastard.