1. (n.) The capacity of a person to handle or absorb aggravation, i.e. "shit." The implication is that when the "shitfuse" runs out, that will be when the proverbial shit hits the fan.
2. (v.) To become strongly adhered to a sitting surface, usually due to extreme laziness.
I'm going to go shitfuse myself to the couch and watch anime until Mom comes home and starts that whole "now that you're 37 I really think you should start looking for a job" bullshit again. Man, that's really starting to burn down my shitfuse.