Essentially, you do everything in your power to get more cards. Literally everything. Up into 20 - 40 cards, just get as many as possible. Then, not only +2 or +4 the hell out of your soon-to-be ex-friends, also use 0s and 7s to switch your decks so they get stuck with an insane amount of cards. Do your best to use 7s to get the smallest deck and then continuously grab cards. Just keep inflating everyone's deck as much as possible.

1. Eventually, once you're 30 to 40 minutes into a game and your friends are pissed beyond belief at you, they'll more than likely team up so they can move on with their lives. You're probably able to keep them locked in the game for a while, but chances are they'll eventually get lucky and get their number of cards low enough to win.

2. After a while, there's a decent chance your friends will Alt-F4 and unadd you on Steam, so be aware of this as well.

Other than the counters I've shared with you, this is a pretty good guide on how to make your friends never play Uno with you again. I haven't played Uno in a while because my friends refuse to even speak to me about the game, it's quite unfortunate.

Good luck on making your friends plan your death!