Them both being men isn't what makes this funny. The player being forced to seduce someone they don't find attractive is what's funny. This has been a trope forever. There's, like, three different layers of the exact same conflict/joke in Shrek, none of which include same-sex couples (unless you think Shrek and Donkey are more than just roommates).

The real offense here is a DM stripping agency from their player for a laugh. The player is clearly not being a good sport about it, and this type of behavior can feel like bullying and absolutely wreck a playgroup.