Just do it. Breathe through any orifice which suits you. have fun. You cannot afford to worry about what other people think. There will always be people who put you down. That's what you get for sticking your head above the parapet - you get shot at. It goes with the territory. Some of the criticism will be unfair; some will be thoughtful, kindly and constructive - but basically its all a pain in the bum - and should not stop you from singing and taking a good swing at what you fancy.