noun: 1. pathologically incoherent, repetitious speech.
2. incessant or compulsive talkativeness; wearisome volubility.
3. pathologically excessive (and often incoherent) talking
4. Excessive use of words.
When the girl went to the front of the class to present her side of the debate, she froze up and ended up with a dreadful bout of logorrhea, spitting out whatever came to mind and making a total mess of her speech. Needless to say, she got a D-.
There! Now you'll never need to say 'verbal diarrhea' ever again EVER.