One of the first things that came into my head. Loving the appreciation for my BHR prank as well by the way.
From a webmaster standpoint, my favourite moments were momentous occasions like the first time I felt like we had a small community, and the first time we broke "users online" records.
From a normal user standpoint, my god there's been so many funny moments. The original days of Gohan getting into flame wars when it wasn't seen so much. Like when Dolph was threatening Gohan's - then called "Randy Savage" - older brother; that shit was fucking hilarious. Honestly though the actual favourite thing about this forum in my opinion is the banter, and that isn't a specific day, so I can't really list anything really specific as the banter is a daily thing. Itr's hard coming up with specific moments or threads.
Oh, another one is the "proph" one which changed everything to "a smurf" when someone went to post proph. That thread turned into so much gold. "I want to find a smurf" was my favourite post.
Another one is the discussion thread where Dean Ambrose first debuted and we were all going fucking insane.