Definition of pile on:
(v) :
(ambitransitive, figurative) To criticize someone or something in a concerted effort; to add on some additional critique.
(v) :
(transitive, informal) To add or apply in great quantities.
(v) :
(intransitive, figurative, sports) To unnecessarily extend the margin of a winning score.
(v) :
(ambitransitive) To jump on top of someone or something quickly.
(n) :
Nonstandard spelling of pile-on. [An argument or fight in which one side is greatly advantaged by being more numerous or more closely allied than the other side.]