Slang for a period, menstrual cycle, etc.
Makes a largely visual comparison between menstrual blood and that really cool scene from Kill Bill V1 (or any other other massacre, for that matter).
Also refers to the hormonal anger brought on by periods.
Guy/Girl 1 - Oh my god, Jess forgot her pad today, it leaked through the back of her dress...
Guy/Girl 2 - Bad?
Guy/Girl 1 - Yeah, panty massacre... <shudders>