Double Sniper Zoom 
To zoom in twice with a sniper rifle, hit L and then click the right analog stick. 

Tech: Easy turret disabling:
When playing as the Tech online, switch to your grenade launcher and use your 
primary fire on an enemy turret to easily take it out. This also works on enemies, 
but not as well. Also, if there is a room with people crowded inside, use the 
secondary fire with your grenade launcher to gas them all. Fire about two shots in 
the room to take them out.

Telefragging:
This can be done with any character as long as the person you are telefragging is 
on your own team. When you go up to revive someone, immediately after you 
revive them press Crouch to telefrag them. Note: You will lose points.

Quick Turbo Recharge 
If you've used up your turbo in a vehicle and you want it to recharge very quickly, 
get out of the vehicle and hop back in. Upon re-entering, the vehicle's turbo will be 
fully recharged. 

Haul More People on Vehicles 
To get three or more people on each vehicle, and have other players jump on the 
car while it's full. Then, the players on top of the vehicle will need to duck and they 
should stick on the vehicle without falling off.