Brraaaapppp:  The most commonly used word in the mx world.  Usually we do this when we're bored and just want to express ourselves.   

Endo:  Front of the bike diving down in a crash usually causing rider to go over the bars.  Usually used in conjunction with "wad" or "ate shit." 

Loop Out:  Opposite of Endo.  Front end goes high and rider jumps off back.  Usually occures with entry level riders off jump.  Most commonly followed by laughter.

Wad:  To crash or screw something up in a big way.  Usually used as a warning.  Example "don't do that jump or you'll wad it up."

Arm Pump:  Occurs when a rider is out of shape or uncomfortable on the bike and his forearms get all stiff and feel like they're going to blow up.  Hard to explain unless you've experienced it. 

Wiskey Throttle:  Usually occurs shortly after arm pump when rider accidently grabs a handfull of throttle when he shouldn't have.  Usually occurs in corners and is followed by an Endo. 

Yard Sale:  A hard crash resulting in the bike cartwheeling and leaving parts across the track.  Usually occurs in the first turn or on straight aways.

Seat Bounce:  The art of sitting off the face of a jump and using the suspension as a pogo stick to clear jumps right out of a corner.  When entry level racers do this it is usually followed by an panic rev and an endo.

Panic Rev:  Usually done while edoing off a jump.  A rider gives the bike full throttle and hits the rev limiter in a pathetic effort to save their ass.  It usually does nothing for the rider but fans are able to follow the sound and watch the crash unfold. 

Rev Limiter:  As far as the bike will go in the rpm's before it blows up.  Fast riders bounce off the rev limiter all the time to keep rpms up while in the air.  Most people just bounce the bike off the rev limiter (especially 4 strokes) because it sounds good.

Whip:  Leaning off the side of the bike on a jump and laying the bike over in the air.  Not to be confused with just sticking your ass of the side of the bike. 

Swap:  Occurs when back end kicks violently from left to right.  Usually occurs in whoops sections or long rough straight aways.

Whoops:  Section of track with large bumps the a rider has to skim over as fast as possible.  Endos, panic revs, rev limiters, and swaps are usually found here.

Case:  Coming up too short on a jump.  Usually occurs with a panic rev.

Over Jump:  To jump passed the landing of a jump and landing on the flat ground.  Usually is followed by a rider walking funny from smashing his balls.

Triple:  A jump that has a take off and two landings.  You can double it and land on the first landing or jump the whole thing at once.  Usually found on arenacross and supercross tracks.

Motocross:  Outdoor races that usually have longer lap times and last longer. 

Arenacross:  Indoor racing that has very short lap times and is held in arena's and at fairs.

Supercross:  Indoor racing that is held in football and baseball field size stadiums. 

So now when someone says "This guy was racing arenacross and seatbounced a triple but cased it and wadded it up"  you'll know exactly what they're talking about.  Brraaaappp

DO NOT TRY THIS AT HOME,,, OR ANYWHERE !!!!!!