I shit my pants out

The speaker (and contributor) was saying to his girlfriend that he might order a chicken fried mushroom sandwich, but if he did, they would have to hurry home before “I shit my pants out”. He immediately realized he had conflated the phrases “shit my pants” (to be very surprised, or literally, to defecate while still wearing one’s clothing) and “shit my brains out” (defecate a lot). Hey, it’s a bonafide malaphor. Props to Adam Jacob for this excellent mashup (no visual there).