Yup, basically as the title says, insult the avatar above you!
*PLEASE NOTE*
By insult I don't mean be cruel about someones avi!
I mean a light hearted comedic insult!
For example, if the avatar above was brightly coloured you could say:
'Ewww! You do realise skittles are for eating not wearing!'
Also, try to make the insult relative to the avi above.