My favorite thing to do when I was a monk was walk on water or walls. My DM would tell me that I could not end my turn while walking up a wall and that I would need to roll an athletics roll to hold on. I would retort Nuh uh, because that is bullshit.

My buddy was recently a rogue that could get surprise attacks in shadows. He would jump from shadow to shadow. We were in the underdark. A cabin was in the middle of an open cavern, it was well lit by lanterns. Said friend wanted to jump from porch post shadow to porch post shadow until he was in the shadows of a rocking chair where a sleepy enemy sat. DM and buddy got in a 30 minute shouting match countering each others argument with bullshit.

I had an echo knight once. Could leap and teleport onto ledges and escape prisons. DM got so flustered that he was the one that called bullshit. Character was promptly incinerated.

DND nights are fun.