The craziest kill I've ever seen was one time when time when I was playing as a sniper with the huntsman bow. It was on the 2Fort map, and I was standing in one of the doorways downstairs in my team's fort. I shot an arrow towards an enemy soldier on the other side of the bridge. An enemy pyro reflected it back towards me, and another pyro, on my team, somehow managed to reflect it again, and it ended up killing an enemy player.
 
The craziest kill I've ever done myself was, again, on the 2Fort map. As a demoman, I was shooting grenades across the bridge, towards a couple enemies on the other side, to prevent them from crossing. After a short fight, with some help from my teammates, the enemy's retreated into their fort. Just then, I thought about the possibility of shooting the grenades over the roof of the bridge, instead of rolling them across the bridge, so the enemies couldn't see where they were coming from before they landed. I aimed for the sky, shot a grenade into the air, and, with perfect timing, an enemy engineer comes running out of his team's fort. My grenade lands right on his head and kills him.
 
What are some of the craziest or funniest kills you've seen or done in Team Fortress 2?

Sniped a guy in the face at the top of his rocket jump arc.  That was awesome. 

In an XPL match I was playing huntsman sniper and pre-fired and killed a solly all the way across mid on badlands.

Not so much a kill as much as it was a moment, but I was playing a heavy, with a very smart medic I might add, and we went invul right as we came to any area where the entire enemy team was held up. It was a massacre.

On some payload map as a medic I got separated from my team when they came down with bullet in the face syndrome.  I doubled back to the an enemy's favorite sniping post and got out the bonesaw and the last thing he screamed was OH GOD STEALTH MEDIC

This was on Gravelpit B. I was playng Sniper with the traditional sniper rifle. There was a demo who laid a sticky ready to sticky jump to the roof. I managed to shoot him in the body without killing him like a milli second before he detonated. He was already so intent on doing it that he didn't have time to react to the fact that I'd taken a chunk of his health and he ended up blowing himself up. I laughed all the way to the organ donor clinic.

I WAS ON FIRE AND I THREW UP ON SOMEONE AND THEY STARTED ON FIRE AND THEY DIED. No but really, I jumped in the air and hit some dude with a bat in the face

I was playing Spy and I got a Medic to latch onto my disguise. 
 
I led him into a train.

As a Spy I was airblasted by an enemy pyro across Doublecross and just when I was about to land I backstabbed a Scout.

Disguised spy walked into my stray rocket and died once.
 
That was pretty funny.

" W + M1 using this i got a 7 killstreak I was shocked actually on how well it worked. "

The best kill I've seen was when a spy backstabbed a demo in mid-air.

An enemy Soldier fired a crit-rocket at me, and I reflected it into a cloaked spy standing ahead of me.

I usually play sniper.  I've got some unreal sniper kills, just complete twitch reactions that end up with my dot on their face.  Nothing that stands out as too crazy though.

While trying to improve my mediocre Spy skills last night, a Pyro decided to juggle me in the air with his air-blasts for (literally) 10-15 seconds instead of outright killing me (which he could've easily done, as I had 16 health at the time). Humiliating and trolly, but also incredibly amusing. (In retrospect, I should've pulled out my revolver and started taking shots at him, but being quick-witted in vidya gamez is definitely not my forte.)

Too many to mention, one that will always stick in my head though, is my first even huntsman kill, pinned a heavy to the wall by his head while he was mid jump. Dosnt seem so special now, but back then, it was the greatest thing i had ever seen/done in that game.