When a guy approaches a girl and asks for her number, but she POLITELY turns him down, why is it a MUST for him to comment on her looks or sexuality; 'You're ugly anyway' or 'What, are you a lesbian?'
No sir. In no way does my lack of attraction and interest in you, change the way I look in the slightest, as I seem to recall only seconds prior you were drooling over yourself with your friends watching me. And, No Sir. In no way does my polite rejection of your (rude) proposition, indicate that I may 'play for the other team', I am just as heterosexual as I was before you approached me.
If you really wanted to get a girls attention in a positive way, how about approaching her WITH A SMILE (and your trousers hitched all the way up to your waist - where they are supposed to sit) and striking up a conversation. Maybe she will turn you down, (but she will be all the more flattered), or maybe she will respond and converse with you. Rather than asking for her 'digits', how about ending the conversation with a simple, 'maybe I'll see you around', and if she took interest maybe she would make the effort to show up in that general area in which you first saw her.
It's not too hard to make a good first impression, but a woman likes to feel wanted and special, trying to get her number and then insulting her when things don't go your way, is not going to cut it.