I have a wonderful cabin crew member (Liam, I believe was his name [to comply with FT rules]), who asked me the same. Wasn't actually in the need of anything (it was 0640 on a Monday - I just wanted to sleep). I suspect if I had asked for a tea or coffee, one would've been provided.
Rule of thumb - ask for nothing more than you wouldn't mind paying for yourself, so no offence is made or taken.