I ended up being "that guy" earlier this year, and I didn't enjoy it.
The campaign had basically gone off the rails. We were on a side quest of a side quest of a side quest that was an offshoot of the main story that the campaign had started on. We also had a problem player that (we suspected at the time but would later confirm) was communicating with the DM outside of the game to push storylines that gave him the spotlight, and to get game info ahead of the rest of us. That player was a wizard that would go nuclear at every encounter, then whine until the party long rested. My cleric had spent the last couple of combats holding back in a big way. Primarily because I was trying to be conservative with spells assuming we would have more combats a day than we did, but admittely also because my character had less and less connection to the story. At the end of the last session I had taken a bit of ribbing, both in character and out, about my character not being much of a team player.
At the start of the next session we immediately got pulled into another side quest, lead by the aforementioned problem player. Vaguely, it involved pretending he was our boss and a powerful Red Wizard to impress some NPCs so we (he) could befriend a group of yuan-ti that were in a civil war with other yuan-ti, which would somehow get important intel about the location of an item for another different fetch quest we were on (that also had little connection to my character). I immediately knew my cleric was barely a side-kick in this side story, and I would have no meaningful role in it. I hit a breaking point and basically went on a short "What would my character do?" rant to he DM. I questioned why we were talkinig to the yuan-ti, why my character would want to get involved in their war, why we trusted anything they said, what reason we even had for being in the area, what my character's motivation was supposed to be, how any of this related to the main quest, etc. It ended with me basically saying that I might as well sit out for this session, because "that's what my character would do".
To the DM's credit, he stopped the game, talked a bit with the group, and offered another side quest via an NPC that was blatantly dropped in to get us moving back towards the main plot. The group took a vote, and took the new hook (abandonning the yuan-ti plot). The next part went a bit better. Unfortuantely, the game was still rapidly deteriorating and eventually ended up crashing and burning hard.
In retrospect, that entire "That's what my character would do" moment was just one symptom that the game was doomed for multiple reasons, and there was nothing that was going to save that gaming group. But I didn't know that at the time; I was still trying and failing. I would like to say that I was doing my best in the situation, but I will also say that I could have done better with the power of hindsight.