The phrase uttered by a seriously constipated person as a good-luck expression just before trying a waxy suppository for the very first time (typically one you steal from your grandma's medicine cabinet).
20 minutes later, you find out how fuckin' wise grandma actually is.
Molly: (whispering) ....Fire in the hole ....
(20 minutes later, after Molly shits her colon inside-out and rinses it in the sink)
Grandma: (Knock-knock) ....Oh, honey, run the fan and light a match.