If your whole deck is printed someone might be a dick about it but otherwise fuck them if they have a problem with a bunch of fake cards. Most good decks (that other people would enjoy playing against) only have about a dozen of the expensive cards so it's really not that many proxy cards anyway. Playing against a deck that's filled with a bunch of $100+ cards sucks ass and will not make you many new friends.

I usually just tell people I have the real card in another deck (I don't). It's really common for people to proxy expensive cards that they like to play in all their decks.

For example, there's a guy at my lgs who plays there multiple days a week and he has a maze of ith in every single one of his decks. He has a literal briefcase full of decks so he would need at least 20 copies of that one card. You can find versions of it for around $5, which isn't that high as far magic cards go, but it's way too much for anyone to own multiple legit copies of. So anyway I've only ever seen him play proxy versions of that card and no one cares in the slightest. Everyone just kind of assumes one of his decks has the real one.