If you touch your girlfriends friends penis is that cheating?

Yes most certainly. If your in a monogamous relationship you should not be physically touching anyone unless of course it is a friendly hug or kissing a family member. Answer: No it doesn't if you do it by accident. Tell your friend that you touch his penis. If they go hostile well looks like your friends nuts. No. Not unless the touching led to some kind of sex. Just touching someone's penis is not the same as having sex with them.