Step 1: Figure out WHY they banned it.
If they're deliberately fucking with you, dodge. Life is too short to knowingly play with trolls.
If they made a mistake, get over it and play another champ for your role. Mistakes happen, especially when you play champs that often get auto-banned like Yasuo. People are so used to banning it every game that they forget to check if their teammates are hovering it. They messed up, but you have nothing to gain by punishing them for a mistake.
If they simply think your pick is bad for the team... Tough call. Teemo is in an awkward place right now, since he's not a great team fight champion and doesn't have much utility beyond dueling somebody in lane or annoying the crap out of people. I'm certainly not thrilled when my teammate picks Teemo. Your teammates should still respect your desire to play him, but it's up to you to decide an appropriate reaction.
But trolling, counter-banning, or int feeding are simply not good responses. You're screwing yourself over just to get back at your teammates. Either suck it up, or dodge. There aren't any better options.