Internet pest (5)
I believe the answer is:
troll
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">internet pest</span>' is the definition.<br/ ><span class="explanation-format__explanation">(abusive or irritating internet user)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for troll that I've seen before include "Folklore monster" , "Fish with a moving bait" , "Ugly Norse dwarf" , "Grotesque dwarf" , "Fish by trailing a baited line" .)