You perform taunts by pressing
(down on the D-Pad).
Triple H is a great option for this as he can do a lot of taunts in a short space of time.
To make this easier, do this while your opponent is downed, during multi-man matches while no-one is targeting you, or during the alligator animation on the Everglades battleground (my personal favourite).
while facing your opponent, walk to the left or right of the ring and press
to toss them towards the alligators. If you're successful, you'll get plenty of time to perform the taunt to completion.
Or use a second controller.