It is a convenience store, there is no other line.

Both were in error.

She was in line first, but she shouldn't even be in line because she hasn't decided what she wants yet. I see this dumb ass rude behavior often. Then, because she was pissed, she went out of her way to be a bitch.

He was rude for trying to cut in front of her because she didn't know what she wanted and he was ready. Then he kept picking at her although he knew he had pissed her off.

Both were assholes, he didn't have that coming though.