Green’s Dictionary of Slang

diarrhoea n.

SE in slang uses

In compounds

diarrhea-mouth (n.)

(US) a very talkative individual.

[US]K. Brasselle Cannibals 84: Jonathan glanced at the diarrhea mouth and stopped it dead with ‘We have no trouble remembering his name’.
[US]Lieberman & Rhodes CB Hbk 127: Diarrhea Mouth — Constant talker [HDAS].
‘The Diehard’ at [Internet] [The] NY Post is not exactly honored for telling the truth. Isn’t their main source of information the Moonies? Would anyone sane put it past them to try to boost Diarrhea-mouth’s sagging ratings?

In phrases

diarrhea of the mouth (n.) (also diarrhea of the jawbone, ...jib, …of speech)

(US) excessive loquacity.

[US]‘Bill O. Lading’ You Chirped a Chinful!! n.p.: Diarrhea of Speech: Talk too much.
[US]R.F. Adams Western Words (1968) 92/2: Diarrhea of the jawbone A cowboy’s expression for talkativeness; running off at the mouth.
[US](con. 1943–5) A. Murphy To Hell and Back (1950) 30: Aw, shadup [...] you got diarreah of the mout.
[US](con. 1920s) ‘Harry Grey’ Hoods (1953) 211: What have you got, diarrhea of the mouth [...] Don’t you ever close that trap of yours?
[US](con. 1960s) D. Goines Black Gangster (1991) 130: And that goes for any of you that might get diarrhea of the mouth.
[US](con. c.1970) G. Hasford Short Timers (1985) 163: I guess all this humping has given me diarrhea of the mouth.
[US]‘Iceberg Slim’ Airtight Willie and Me 40: We might give some jokers in the joint diarrhea of the jib if we split together.
[US]J.L. Gwaltney Drylongso 234: That joogie was bawn with diarrhea of the upper and lower lip!
Grants Pass Daily Courier (OR) 6 June n.p.: ‘Constipation of the mind and diarrhea of the mouth,’ were the courtroom words hurled down from the bench by an out of town Judge.