Is your date a little too friendly?

Whenever you bring your friends or family around the person you are dating, there is a possibility that things can go awry. Someone could tell an embarrassing story about you. That annoying nickname from childhood is used and you have to explain why adult people are calling you Poo Bear. Then there is the rare chance that your date is a little too friendly.
This was the case for my friend Randy last weekend. The Memorial Day weekend was filled with graduation parties and cook outs. Randy was introducing his new woman for the first time. When she met some of his friends from childhood, she was smiling and friendly. Then it began to get uncomfortable when she was flirting with them. This is a big no no, in his book. He asked me was she trying to make sure that his friends liked her or was it something else.
I said it was something else. Like, perhaps she isn't truly interested in him as much as he thought. I think checking out someone else when you are around is bad enough. When you are outright flirting with them, you are just being disrespectful.
Have you ever faced this situation? What would you do?