grow a tail meaning (humorous): definition

grow a tail

verb

Etymology * All three meanings are related to defecation, in three different ways. * Grow comes from the ideas of expansion (after emergence), either sudden (as in senses 1 and 3) or gradual (as in s. 2). * Tail refers to the fecal matter itself, namely its shape (especially that of a “log”; and esp. in sense 3) and the side of the body whence it is expeled (the back side, where a tail would have been located).

Euphemistic, Humorous, Idiomatic, Mildly, Slang, Vulgar To defecate; to have a bowel movement.

When man needs to grow a tail, man must run to bathroom without fail. Thou shalt groweth thy tail with great care, or though might staineth thine underwear!2000 Larry Glanz The Ultimate Book of Bathroom Etiquette and Humor pg 146 and pg 152
Kathy is teasing Dad that Mom is growing a tail in the toilet. Guess he understands to a degree and had a strange look on his face when I came out, so assure him I am fine and did not grow a tail.2009, Ann McDeed, No Greater Love, page 206:

2 more examples

A steaming pile of toilet humour might not be everyone's cup of tea, but there's no denying the hilarity in some of these messages from beyond the bowl. Our readers managed to snap these delightful deuces before breaking the seal, splashing the pirate, building a log cabin, growing a tail... you get the idea.2012, Tyson Jopson, Best of Getaway Funny Signs, page 28:
The only other guy doing any work around here was the fat old cop down in the can, strugglin' to grow a tail.2016, Vanessa Hawkins, Gloryhill, page 91:

Euphemistic, Humorous, Idiomatic, Mildly, Slang, Vulgar To struggle to hold back an imminent bowel movement.

Endearing, Euphemistic, Humorous, Idiomatic, Mildly, Slang, Vulgar, In childcare To have a protuberance (a bump) be formed on the rear of one's bottomwear (viz. pants, underpants, diaper, etc.) after an incident of solid fecal incontinence.