He's surprised at the lack of comeback to that; most blondes give him lip when he says something along those lines. It obviously doesn't occur to him that she wouldn't know that blonde girls are there to be made fun of, so just figures he has to try a bit harder.

'Tell me somethin', luv, 'cos I've always wanted t'ask a blonde bird this - d'you put lipstick on your forehead when you wan' t'make up yer mind?'