What should i say when i guy chats me up?

[sunnyD]

Today it was really sunny and warm, and i was walking home minding my own business, and up ahead there was a bunch of people waiting to cross a road, and also three shirtless guys (rather unattractive and overweight, though one of them was ok). When i got to the part of the road where everyone was crossing the pavement was kinda crowded and outta nowhere the ok looking guy stuck his hand out and said 'Hi, i'm Jamie, how are you'. I was a bit caught in the headlights and just stammered something and kept walking, manoeuvring myself through the crowd feeling really embarrassed.

He wouldn't have heard my stammering and i didn't look at him so he'd have thought id just ignored him.

I wasn't interested in him as im taken, but i now feel really bad - was i really impolite, or are guys used to girls ignoring them?

What should i have done instead, bearing in mind that although im not interested, i don't want to be rude?