Ok i'll start.
pick stealing gnomes
a person saying a guitar is out of tune when it's in dropped D tuning. DADGBE
People who forget that playing guitar is supposed to be fun.
People who mess with the settings/knobs on amps,pedals,guitars.
people who play the solo from Stairway to heaven with the distortion on
"That song sucks,play something popular" Grrrr.