Dude— It stinks!
And it's going to keep on stinking FOREVER! Or at least until you get back to Earth. I mean, you can't open up a window for some fresh air...unless you want to get sucked into outer space.
Not only that, but farting in a space ship could be dangerous. Many farts have methane in them, and methane is flammable!
|"Touching Snoopy's nose|
will keep my methane low."
So Murphy suggested to NASA that only astronauts with safe farts should be allowed to go into outer space. NASA didn't listen, though. Instead, it just stopped sending beans and cabbage as food for them.
fine report on the matter at NPR.
2001 picture from IMDB.