Your last question was iffy, assuming for a moment this question isn’t Trollish... Those example words you gave are offensive. You’re “friends” use of them in America would be offensive. Your use of them here is offensive. -1
In any country, offensiveness is a moving target. (But half the fun is trying to use these words in a way that is NOT inappropriate or offensive.) This is a slippery-slope; not advised for a non-native speaker. What you may be picking up in movies is witty New York writers throwing down instances where these terms can be used with relative impunity. Some would say the very purpose of art is to “cause effect”, to push the boundaries. Not advised for your friend - or you - ass face. : )
(That was ironic - I've never seen your face.)
Edit - addition below:
The more I think about it, the more your question is entirely valid.
“BUTT” is not an offensive word; unless you’re telling someone to stick something up theirs. For example, I might chide, “I’m going to smack you on the butt.” playfully talking to my daughter/wife, both knowing it’s an empty threat - fun - (not so much to a mother/grandmother. Don’t do that.)
“ASS” is just a more vulgar way of saying butt. Vulgar, but not reprehensible. (“You’re a pain in the ass.” can be used as an idle, non confrontational, expression of exasperation – playful. But, these things are VERY context sensitive!)
“FUCK” is only for idiotic/ironic/humor; never used outside of friends. (“Fuck that noise - $5.50 for a f’ing cup of coffee?”) Special Note: In almost every single case the use of the “F-word” = bad upbringing. People play with that though - pretending they are The Sopranos or something.)
“DICK” = again, only for ironic/funny use. (e.g. the female character Heather Duke in the movie Heathers (1988) – “Veronica, why are you pulling my dick?” It’s vulgar but not reprehensible.)
“GAY” is tough. There is a lot of leeway with that one because the original usage was synonymous with “happy”, but you have to be sensitive to homosexuals (in an overwhelming Liberal society.) But, I mess with that all the time. “I’m gay for Mexican food.” is a current favorite mantra. But I’m an idiot. You and your friend should not do these things. You can only use “gay” when it is clear that you are not intending it to hurt someone who is actually gay. Reprehensible that.