godan verb (-ku)
ejaculate (usually via masturbation)
Vulgar slang; typically refers to male masturbation. It is a rare term, but it is understood in adult contexts.
彼は一人でいるとき、よく一発抜くらしい。
Apparently he often jerks off when he's alone.
Compound of 一発 (one shot) and 抜く (to extract, to pull out). The exact origin is uncertain, but the phrase is a vulgar slang expression for ejaculation.