Though it can be frustrating, I consider being accused of using an engine the highest form of flattery in online chess. In the following game, I played poorly in the opening and better thereafter.
Immediately after the game my opponent sent me the message, "Very rude and an obvious engine user. Block this one!" By "very rude" I can only assume he was referring to my live chat being switched off by default (naturally, to avoid having to interact with trolls like him). He had already blocked me before I could respond.
In my opponent's defense, one could see how he might assume that after an early blunder, I became angry and turned on an engine (though missing 23. ...Qg3+ might have clued him in).