I was probably about halfway through the assassination animation when the dude's teammate comes to his rescue and pulls me off of him and assassinates me instead. Then the two just ran away together, probably laughing.
I know trying to pull off assassinations in tight quarters is a no-no, but that was pretty cool.
Also, air assassinations feel pretty amazing to pull off. The best one I did was on the circular roof thing on Complex. A guy was jetpacking up to the top and I jumped off and assassinated him midair. Love the feeling.