I generally don't get easily annoyed by people - or atleast I used not to get. Maybe I'm just getting old and cranky.
Anyway, there was this one guy who knew it all before he started. He even knew things better than our sensei. One example that clings particularly well to my memory:
Guy (talking to sensei): "So, does anyone here use a shirasaya katana?" Then he adds to it with a really arrogant style (Because, after all, he (atleast in his own opinion) knew lots of things nobody else knew): "That is, the straight stick sword".
I get a huge urge to point out to him that he is mindbogglingly wrong, but decide to keep my mouth shut and see what our sensei says.
The sensei looks down while continuing to fold his hakama, smiling a bit. After half a minute or so of continuing his folding, he looks patiently up and explains politely that the shirasaya is the storage sheath of the blade, and not a type of sword.
And so, the guy switches to the next topic he thinks he knows better than anyone else.. And this would keep going on forever. I think people like this learned what they know from a mail order catalogue or something and are trying to constantly impress with their superior knowledge. REALLY annoying.