To drink your pint (alcoholic drink) too slowly, compared to the people you’re with. To be named a jibber or ‘jibbing’ for drinking too slowly within your group.
Jibber jabber is Incoherent and unintelligible rapid speech often in slang or patois. Used in the UK as a disparaging name for other languages such as French, Spanish or American.
“It was all jibber jabber. Couldn’t understand a dam’ word the wretched feller was sayin’, Jeeves.”
“But, Milord, he was an American.”
“Yes?”