I had one DM who was a real class act. This was in 2E, and he had every book on earth. He made his own minis, had his own copy machine, wrote his own adventures with color coding for referense... I mean, the guy was an uber DM. I have no idea how he managed to work and live alongside his habi-- er, hobby.
You'd
think a guy like that would have a solid grasp of the rules. Nope.
I can't recall any specific houserules of his, but some rulings that didn't surprise his regular players. Like seventeen gnolls with longspears attack from behind a wall with holes, all of them in 4 squares. A 5' by 20' area.
Or when my character knocked himself unconscious because I slapped a normal spider on my shoulder. He said roll for damage, I did, and did something like 5 points of subdual damage. Out I go! I can't even remember most of his crazyness, thankfully.
A different DM actually was the KING of houserules. It was right when 3.5 came out, and he and his regular players used
every D&D book they had. Social Status from 1E UA, MR from 1E DMG, chances of Wild Talent from the 1E PHB, kits from everything 2E. Specific houserules included rolling at character generation for chances of photographic memory and spellfire, rolling 1d30 (yes, a 30-sided die) for hit location with each individual number being a different location with wacky different effects, feinting as a FREE action and benefits your full round of attacks(!), and on and on.
I only played with them about 4 times, and I never got a handle on their incredible houserules. It didn't help that NONE of them were written down, and each person remembered each obscure houserule slightly differently.
Yet the weirdest thing about that DM was that he was such an
incredible roleplayer. Voices, inflection, facial expression, emotion... the guy could amazingly portray any character so vividly. He could give actual speaches. Like, for minutes(!) without any notes or anything! And I'm talking quality stuff. So was the guy an actor or anything like that? Nope, ex-marine