SinisterDom, my buddy. I'm sorry you gotta go through that. Unfortunately, you can't control what other people are going to say, no matter how ignorant they may be.
The only thing you can control is you, and the way you feel. You know that the ukulele is a wonderful instrument. That's why you chose to play it. Let those other guys say what they want. I know you hear this a lot, but they're just jealous. I'm willing to bet that they don't play any instruments.
So in a few years, when you're dating a hot ukulele-loving chick, they'll be playing Ukulele Hero on their XBoxes, wishing they were you. Then you can smile with satisfaction and tell yourself that you made the right choice.
Until then, take the high road, brother. Don't even honor their ignorance with a remark. Stay classy, keep your eyes on the prize, and you'll reap the rewards of hard work sooner than you think.
And remember there's always a group of ukulele players here at UU who you can turn to. We know what's up.