Gonna have to agree with Voij here.
Feint reduces threat by 2162.
A rogue's threat modifier is 0.71*damage done
So assuming that he's doing 5k DPS, thats 5000*0.71 = 3550 TPS
Assume another rogue, doing 8k DPS, is using tricks on him, for 9 seconds every 30 seconds. That's an extra [9*(8000*0.71)]/30 = 1704 TPS
3550 + 1704 = 5254 TPS on average.
2162 / 5254 = 0.411496
So, 41% of a second's worth of Threat lost. That's not going to be a cause for losing threat on a boss mob.