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