Go bite a bear in the ***-What does this mean?

Okay so I'm part of a trading site and I trade with this one user . This user was very hard to bargain with. She rub me off the wrong side. She told me that was it was rude to not tell people when you get their package in the mail. I did response back however she feels I didn't tell her quick enough. I'm sorry but my life doesn't evolve the internet. I try to response promptly as the best I can but its hard juggling my daily routines and lifestyle. She told me to "go bite a bear in the ***" What exactly does it mean? I feel very taken back by this user. Should I contact a moderator?