Low Tolerance for Rudeness Today

This kind of thing happens to everyone. Last night I went to buy some groceries. I had 9 items and I got in the 15 items or less line. The person in front of me had about 30 items. So they divided it into two orders and paid twice in order to avoid waiting in the slower lines. Not only did they make us all wait because of their larger order, but they made us wait while they paid twice. I guess they thought they could get through on a technicality. Just rude. They knew that they were being rude, but didn't seem to care.
Here's another: On a discussion board, someone asked a question on PC maintenance. I answered with a rather long post giving my advice. I am a PC expert and I make my living giving companies my opinion. I was giving it away there for free. The person answered back "Thanks for your two cents". How am I to take this? Is this a casual use of a phrase or a comment on the quality of my post? It sounds sarcastic to me. It is difficult to tell without facial expressions or tonal quality of a voice. The post did upset me. I did not reply.
Perhaps I am being overly sensitive, but I am in a lousy mood today so don't cross me.