The face you get Post Blow Job (as well as after chomping into a peanut butter and jelly sandwich): a look of pure ecstasy, punctuated by a silly grin. A look of supreme satisfaction.
it's the kind of face a person makes when someone says something utterly stupid, or when you drop something after you were trying so hard not to. It's like a "WHAT THE HELL" face.
You can also say it whenever something dumb happens. It's kind of like a "okay no" sort of face, you know? Everyone makes it a lot, they just never know it's a jface ;)