Not everybody is interested in everything.
Everyone's got their own particular sphere and multi-limbed web of general interests.
When one goes on about a topic that another finds uninteresting, then their listener is bound to get bored, (and boredom is the precursor to annoyance.)

This is where tact comes in. Tactfulness is the ability to read boredom (as well as uneasiness, embarrassment, and any other general anxiety-inducing feelings) in your listener. Someone with tact knows when to change the subject and/or shut up altogether. It's a subtlety.

However, the more passionate one feels about a subject, the harder it is for them to show tact when talking about it.

This explains why nerds and drunks get such a bad rap for being annoying. (God forbid, a drunken nerd . . . )
Because they feel so passionately about the topics that they're interested in that they'll often talk at great length about them without any regard for their audiences' boredom. (And prolonged boredom invariably leads to annoyance.)

This is why the nerdiest of nerds is often regarded as a god amongst their peers (with "peers" in this sense really just meaning people of similar interests.) Because they have such vast knowledge of such a particular subject (which is often of very little interest to most Others. ("Others" in this sense meaning people who are outside of this particular circle of peers.))

The same may or may not be true for drunks.
(Although, there's something to be said about both of them being the most likely to have conversations with no one but themselves.)

This also explains general aloofness (a.k.a. coolness, i.e. "being cool.")
The types who seem so disinterested in everything that people often become interested in them if for no other reason than to simply find out what it is that they actually do find interesting.

This is why cool people tend to be so popular. Everyone trying their hand at gaining their attention by drawing it to this thing or that thing, with a weird need of validation being thinly-veiled beneath it.
(This might also explain why "cool" people tend to be such *******; often dismissing these constant attempts to grab their attention as either pathetic and/or depressing.)

Then, of course, there are the word-smiths. The Salesmen.
Those who fancy themselves so intelligent as to be able to twist what their audience would otherwise find disinteresting into something that they can't live without,
often through some combination of communication manipulation and nonverbal tricks.

But just don't listen to them.