When you're allergic to something, and you get your partner to coat their dick in the trigger, so that you give them the tightest blowjob possible.
Remember to keep your epi-pen close.
See also:
Anaphylactic Blowjob
The Epi-Pen Special Death Grip Deluxe
Allergy Throatlock
PeaNUTbuster
Person 1: My girlfriend is freaky as fuck - she put peanut butter on my dick and gave me a blowjob
Person 2: Wait isn't she allergic to peanuts?
Person 1: yeah she gave me a Peanut Butter Throat Jam, good thing she had the epi pen ready
Adjusting one's cock to make a hardon more comfortable. Usually neccessary as the result of a log jam caused by erotic sights such as up skirt or down blouse viewing. The discomfort of the log jam may force a jam buster in public, in which case it has to be done as fast and as discretly as possible.
I got so darn hard at work the other day looking up this girls skirt, I just had to do a "jambuster" to let my cock stand up. I looked around to see if anyone was looking, then as quickly as possible, I put my hand down the front of my jeans and freed my cock.