KSI Trolls IShowSpeed After WrestleMania Beatdown, 'Sucks Doesn't It?'

Talk about adding insult to injury -- IShowSpeed's pain continued after getting destroyed by Randy Orton at WrestleMania 40 ... 'cause KSI made things even worse by heckling him over the epic ass-kicking.

The popular streamer made a surprise appearance during Logan Paul's match against Orton and Kevin Owens on Sunday ... revealing himself as the guy in a Prime bottle costume.

View this post on Instagram Speed took quite a beating throughout the showdown ... with Orton viciously kicking him and hitting him with a signature RKO, which took him out.

Speed appeared to be in major pain after Paul retained his United States Championship ... wearing a neck brace and lying on a cart.

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Paul's…