IWTSTH rule and the muck

[fellfold]

So I was playing like 6/12HE at Bay 101 and this complete donk shows up to the table.

Example: I have ATo, he has TT, third guy has 88, flop comes A8x. I bet, he raises, third guy raises all-in, I call, donkey caps. Turn is a T, I check, donkey bets, I raise, I get three bet. I check call the river.

Afterward, he says, "I felt the ten coming."
I say, "1-outer."
He says, "yeah, out of 30 cards, that's amazing."
I say, "More than 30."
He says, "Yeah, like 32." I say, "More than 32."
He says, "That must have been like less than one percent."
I say, "More than one percent."

Anyway, this guy is awful, spewing money, and a total douche. What made him more annoying was that he would invoke the IWTSTH rule every river he saw, to see every hand that didn't show. He got to the point where he was insisting if you called a river bet, you HAD to show your hand, regardless of whether someone asked to you to or not.

So I started doing a couple things, mostly to try to tilt the loser. The first was to always ask to see HIS hand. This especially pissed him off when I wasn't in at the river. The second was to regularly pitch my cards into the middle of the muck. (I was sitting right next to the dealer).

When I pitched my cards into the middle of the muck, he would occasionally go ape [censored] and even fish through the muck. Is a player actually allowed to touch the muck? Also, if I fire my hand into the muck, can the dealer still fish it out and show it?