Wow...that was a pretty disrespectful thing to do. And what adds to it is the fact that he did it right in front of you. Don't worry though, one day that guy will take 1 liberty too many 😉.
the guy could also not have known what it meant. they could have been friends, friends do tickle eachother with no ulterior motives sometimes. it happens. not everyone views things liek we do. hehe