Tank at anything considered “high level”.
I once almost ruined a Tribute to Insanity run filling in for a tank that was sick. I messed up the rotation on H Anub and just the fear of tanking it all for the first time was so stressful. I just haven’t done it seriously ever since, I’ll do it to mess around on alts, but ill never offer to fill in that role again in like a main run.