Charge about right for offensive online poster (5)
I believe the answer is:
troll
'poster' is the definition.
(I have seen 'Provocative poster' mean 'troll' so perhaps 'poster' could also mean 'troll')
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for troll that I've seen before include "Dwarf (or giant) of Norse myth" , "Fairytale monster" , "Scandinavian monster" , "Online pest" , "Dwarfish creature" .)