Some people make a bad first impression because they care too much about making a good one.

Effort shows up as stiffness, and stiffness reads as something else entirely. Somebody who desperately wants to be liked goes quiet, or talks too much, or says the rehearsed thing, and the room files them as arrogant or cold when the actual problem is that they cared too much to be natural. The impression is an inversion of the cause.

This cuts in both directions. Give the awkward person a second meeting, especially if the first was a situation designed to make anybody tense. And when it is your turn to care too much, remember that trying to be impressive is the thing getting in the way.