Way back in the day my dad played Descent online all the time. I was not any good at it, but I thought it would be fun to try playing it. I joined in a game, began losing badly, so I thought it would be funny to enable cheats. This is back in the day when you could just enter console commands for cheats on PC, even when playing multiplayer. However, whenever you entered a cheat it would be announced to everyone else who is playing. They were not happy about it, LOL. I think I gave myself unlimited mines or something like that.
Other times, I was not cheating on purpose, but I would guess it was a cheat.
Back in the days of Dreamcast, I had the mouse and keyboard for it. Playing Quake III online with mouse and keyboard when almost everyone else was on the shitty Dreamcast controller, really gave me an edge. If you think today's m&k players have an advantage over those with controllers, you need to do it back when the controller did not have dual anaglog sticks LOL. I would dominate all the time, giving me a false sense of skills.
Similarly, playing Unreal Championship 2: The Liandri Conflict on the original Xbox, if you were the host you had a major advantage in that game. Well, we had super fast internet at the time, more than most, so for the majority of the games, I was the host. I would wipe the floor clean due to this. Not cheating really, but not fair to the others either.
Not talking about online games, I loved using Game Genie on NES and SNES and GameShark on N64. I did this mostly to help me complete games that I would rent. When renting games, I would make sure I had cheat codes for them, so I could complete them within the rental period if I could not do it on my own. I would also always use it to play through Contra III: Alien Wars and Final Fight on SNES. Even though it was cheating, I had fun as a kid, playing through them over and over again with infinite lives.