Lol, I don't think they actually mean to p!ss people off. They are just living their lives.
But, yes they are annoying to have in your house.
I actually made a how to on how to get rid of flies in your house, check it out! :) http://www.funadvice.com/howto/ridflieshouse_coming
Because they don't live very long.. so they figure they might as well have fun with what little time they have left. :P
i dunno bt i totaly agree wit u thers so f..king anoying!!