I totally hear this one!
One of the only times in my life I've gotten into a screaming match with someone was at Wal-mart. (The other was a coke-head x-employer) Someone decided I was taking too long at the customer service counter and thought it would be a good idea to start talking very loudly about how rude *I* was to everyone in line behind her. She had no idea what was going on, and the delay was definatly no fault of mine, on top of the fact that another employee at the counter mysteriously disappeared while there was a line forming. I guess she was just pissed in general that day because someone dropped a house on her sister.
I got right up in her face and told her exactly what I thought of her and which orifice she could stick her ignorant opinions in. I don't think my husband's ever been prouder of me- lol!
The huge-group-standing-in-the-middle-of-the-aisle-talking thing is a huge pet peeve of mine. Friggin get out of the road already!