Smee again.
A real pet hate of mine is the overuse, or incorrect use, of 'like'. Listening to the (mainly) younger generation makes me wonder if they put their brain into gear before their mouth. For example: I went out, like, for a walk and, like, went to the shops to, like, get something to eat, like, you know, and the guy behind the counter was, like, really weird...'
Also, as mentioned by others above, one has to wonder how people make it through school, let alone university. I was once in the collections office of the Australian National University in Canberra when fees were being collected. There was this student re-enrolling and was writing a cheque. I was floored when he turned to me and said "Excuse me mate, do you know how to spell 'hundred'".
I know I am far from perfect, and I am often guilty of incorrect grammar or punctuation, but I do try to ensure that I am as clear and unambiguous as I can be.