To have performed sexually at such a profound level that the utilised orifice has caught fire due to friction.
This could be down to a number of factors:
1. Overly
fricative appendage surfaces, e.g. a
scaley penis
2. Use of a lube with an insufficient smoke point for the activity, e.g. high-velocity anal sex lubricated with Butter (
176°C) rather than Ghee (250°C) that meets an emulsifier, e.g. 'Baby Gravy', thus overcoming a natural fire
retardant, e.g. 'Fannybatter'
Example 1 is pure friction but usually occurs before Cum enters the picture so is not relevant to this analysis
Example 2 is the true Cumbust in that it is down to the complex chemical interations of these substances when extreme kinetic energy is applied to them
Example:
Bob - Jesus, did you see what happened when Bill banged Brenda's Bum hole?
Babs - Nope, wtf?
Bob - She
Cumbusted, flew into low earth orbit, left a trail of
winnets in the night sky that looked like a
meteor shower
Babs - Shit, talk about blasted into maternity by a guided muscle....