How do you feel up your girlfriend in the cinemas?

My mate was talking to my gf, and he showed me the messages, and they were talking about when I should feel her up. My gf was saying at my or her house, but people are always there, so we wouldn't be able to do it really. My mate then suggested that I should feel her up in the cinema when its dark and no one can see you. So basically just wondering if anyone has any hints on how I can feel up my gf in the cinemas