People who say "Can I get..." when ordering coffee/sandwiches etc. I know it's trivial and it shouldn't wind me up but it does
I'm guilty of this. I try so very hard, thinking all the way through the queue "say can I have, say can I have" then get to the front and "Can I get..." slips out.
Having said that, in recent weeks I've found I've been overcoming this and am managing to say 'can I have'.