also: こてんぱ
adverb
completely; thoroughly; to a pulp
Mimetic adverb used with verbs of beating, defeating, or criticizing to mean 'utterly' or 'to a pulp'. Often collocates with やっつける, 負かす, やられる, etc.
昨日の試合で、相手チームにコテンパンにやられた。
We were completely beaten by the opposing team in yesterday's game.
He was thoroughly defeated in the argument.