pejorative language - What is a negative word to describe people that love showing off their knowledge?

A "Clavin" is dated but still funny. Cliff Clavin was one of the main characters on one of the most popular sitcoms of all time in the US - Cheers. He is the EXACT person that you describe in the most extreme way.

Terms I would use to describe Clavin would be:

1. Windbag


2. Bigmouth


3. Blowhard

Clavin Quote #1:

Well ya see, Norm, it's like this. A herd of buffalo can only move as
fast as the slowest buffalo. And when the herd is hunted, it is the
slowest and weakest ones at the back that are killed first. This
natural selection is good for the herd as a whole, because the general
speed and health of the whole group keeps improving by the regular
killing of the weakest members. In much the same way, the human brain
can only operate as fast as the slowest brain cells. Excessive intake
of alcohol, as we know, kills brain cells. But naturally, it attacks
the slowest and weakest brain cells first. In this way, regular
consumption of beer eliminates the weaker brain cells, making the
brain a faster and more efficient machine. That's why you always feel
smarter after a few beers.

Clavin Quote #2:

CLIFF CLAVIN - You know Rebecca, I don't know why you're so concerned
about your figure. You know, back in the Renaissance times, full
figured women were revered.

NORM PETERSON- Get out.

CLIFF CLAVIN - It's true. Yeah, yeah, artists would only paint big,
voluptuous women. In fact, that's how they got rid of a lot of their
old paint.

Clavin Quote #3

You know, there's a lot of misunderstanding about rats. The rodendus
vermikitis as they're called in Latin. It turns out our long tailed
friend wasn't after all responsible for the dreaded bubonic plague as
alleged through history. Yes, sir. It was caused by an animal called
the bubon. That's right, and the threat by the way is still with us.
So if anyone does see a bubon, contact your local authorities.

Clavin Quote #4

Norm, it's a little known fact that the word Florida comes from the
language of the Okie Canokie Indians and it means, literally, place
where the old people come to sweat.

Clavin Quote #5

You see Sammy, topless waitresses, scientific fact, they can deliver
drinks faster than their clothed counterparts.