It's very brave to post something for strangers to see but don't be disheartened. Nobody and I mean nobody writes good first drafts. Don't take it personally it just is the way it is. Water is wet, first drafts are pretty shit.
It's great your friends find it funny but friends:
a) Are not comedy commissioners
b) Are friends and so will be nice you, otherwise they wouldn't be friends (unless you have instructed them to be honest and they are stupid enough to be honest!)
c) Are not going to sell their houses to raise the £150,000 - £300,000 an episode it takes to make a sitcom.
If you want to be a writer you have to learn to take, even love criticism because you will get lots of it much more than anything else (including success). You also have to study sitcom and know why sitcoms are successful. There is a link between all successful sitcoms and if you want to be a serious comedy writer you have to attempt to understand what that link is.
Unfortunately sitcom writing is probably one of the most difficult crafts to master. It's no different than any other skill. You have to practice, practice, practice, study the great exponents of that skill and then even after that there is no guarantee that you will have that certain something that will make you stand out from the crowd and persuade somebody to invest hundreds of thousands of pounds in you.
Of course if you're doing it for fun and for your friends that's great. If it gives others pleasure then good on you. But if you seriously want to be a comic writer then you need to not just expect criticism but welcome it with open arms.
My advice would be to go back to basics (skip the basics and you will never ever develop as a writer), buy some sitcom books, go on a sitcom course (like the sitcom mission course), keep your sitcom idea on hold ( many writers keep ideas on hold for years that eventually get made) give yourself time to get the basic foundations and then you will be in a position to write something that could start you on the road to a professional career.
Oh and there are loads of people who want to write sitcoms, and do, and yet how many great sitcoms have you seen recently? So just remember that writing a great sitcom is absolutely pretty damn impossibly difficult and anybody who says different is either delusional or lying. But hey that's the challenge! And if you crack it, then you will be showered with praise and worshipped and be able to work in America. Until then it's just criticism I'm afraid!