When a man ejaculates rapidly, unexpectedly and with greater-than-average force and velocity into the unwitting face or forehead of his girlfriend / wife / partner, thus leaving them with a stunned expression.
This is inspired by the captive bolt pistol that psychotic killer Anton Chigurh uses in the movie 'No Country for Old Men'. His victims have no idea what's coming and when they do it's too late.
The device itself is usually used to stun cattle or livestock before they are butchered.
"Man, my girl was giving me the best BJ last night and before I knew it, I'd totally fired a captive bolt pistol right in her face... she was pretty stunned!"