when i was starting out with 40k i went to a friends house to play and as we were having a game his mate came over and wouldn't stop telling me how shit eldar are (i was playing eldar) and how good marines were (the other side was marines).
it was so annoying he wouldn't stop going on about their superiority and how my units would not do the job i was doing with them.
this guy was so annoying, he kept telling me about rules that i knew and that he obviously didn't, and was going on about using characters from different dex's in his, for example using Canis Wolfborn as his HQ for his ultra marine army.
and i had to just listen to this shit for hours.
and when i mopped up the entire marine army with little casualties to my self, he went "your just lucky, you should play my army"
i wanted to crack the Muppet in the face so bad.
the other story i have is my first 40k game i had, i went to a GW store with a friend (also new to the game) and the guy in the store stood basically playing for my mate and when ever it was my turn didn't even give any tips to me at all, he even let me target units that he knew once i rolled i had no chance like s4 weapons against a dread.
come on i asked the guy to teach me how to play and i got raped.