"are you all right there?" when they mean 'can I help you?'
it makes me feel like shouting 'DON'T I LOOK ALRIGHT? WHAT ARE YOU SAYING YOU FUCKWIT? ARE YOU SUGGESTING I LOOK WEIRD OR SOMETHING?'
but of course i don't ......(or else they could have a point!
i often say 'fine thanks and are you all right there too?' which makes them a bit 
another one that grates a bit is for example they put a coffee in front of you and you say 'thank you' and they say NO WORRIES!!!
GRRRRRRRR!!!