How do you feel about random people touch your partner, if you know that they don't like to be touched?

I was in a club with my girlfriend and while I was gone a guy started to talk with her.
She introduced me as her boyfriend to him and the guy kept talking with her and while talking he would touch her back or her arm.
I found this very weird. She didn't notice that much and she does not know if a guy is flirting with her.
What do you think?
How do you feel about random people touch your partner, if you know that they don't like to be touched?
Post Opinion