This is a really strange question

But how do you bring up the movie My Big Fat Greek Wedding to someone who is Greek without being offensive?

In what context are you bringing it up? I think it depends. If you say you believe that stereotypes portrayed they’re accurate, it’s offensive. If you just say it’s a silly little comedy, then it’s fine.

Also if in doubt, just don’t bring it up.

Yeah like i wouldnt ask to borrow their Windex.

I think as long as you’re being casual and not making assumptions about their culture based on the movie, it should be okay. It’s a well-known comedy, so bringing it up in a lighthearted way (like mentioning you enjoyed it) probably won’t come off the wrong way. Just avoid using it as a reference for "how Greeks are," and you should be fine. Context really is everything.