(v.) To lose one's cool; become really pissed off. The idiom is in reference to a
pressure cap popping off, usually resulting in a nasty burn or imminent explosion. Thus, the person who caused the
pop off is about to get told or be destroyed, depending on the nature and severity of the inflammatory incident.
James: Vernie, your little wigga child is uuuuugly.
Vernie: No you di'int, heeeyll no, heyell no, heyell nah, heyell no, you said what, naaah, heyell no, heyell no, heeeyeeeell, no, etc.
{Vernie has popped off at James' comment}
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Boss: Dave, I know you're a family man, but I need you to come in Saturday... aaaaand Sunday, and stay late every
night this week.
Dave: That's cool boss, I'm just gonna need your
head in a
fucking drill press while I go to work on your
nuts with some bolt cutters and run an arc torch down your spine after I've nailed your
feet to the floor with a remington power driver.
Boss: Okay Dave, no need to pop off now, I'll get Clarence to do it.