In MOBA games, it refers to dodging a projectile before it was shot by the enemy by leading the enemy in a direction, then changing directions before the projectile is shot, to fake your direction so the enemy leads the shot in the different direction. It is opposed to 'dodging' because 'dodging' implies there is a projectile already shot that has to be dodged.
Juking = dodging a projectile's direction before it has been shot.
Dodging = dodging a projectile after it has been shot.
It's when someone follows to get a follow back, followed by an unfollow that leaves the followed unfollowed.
Similar to the American Football / Basketball move "juking" - when someone thinks you're going left or right and you move the other way, leaving the pursuer empty handed.
Mike follows Lisa, Lisa follows back - Shortly after, Mike quietly unfollows Lisa, leaving his follower count one higher and Lisa thinking she has a follower she doesn't.
"Dude, I was just twitter juking and I juked about 300 people... they followed back and I left them high and dry... "