insult to mutter when one or a group of SERIOUSLY badly dressed people walk by.

Basically you are insinuating they must be in fancy dress to look so ridiculous, hence 'what did they come as?'
50 yr old woman walks by with big clunky black leather boots, a vile patterned multicoloured gypsy skirt, jewellery made from old christmas decorations and a t-shirt 3 sizes too small that says 'babe' on it:

me: what did they come as?
by me old fruity July 2, 2006
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