Is there a less colloquial word (noun or adjective) to describe an "attention whore"?

It could be a noun or an adjective, and either could describe a person or an action. For example:

"Did you hear Eric's wedding toast? He wouldn't shut up!"

"I know, he was being a complete _______"

Solution 1:

Consider attention seeker. (or attention-seeker)

attention-seeking (adj) Attempting to attract the attention of other people, typically by disruptive or excessively extrovert behaviour

You can also use ostentatious

: marked by or fond of conspicuous or vainglorious and sometimes pretentious display

: displaying wealth, knowledge, etc., in a way that is meant to attract attention, admiration, or envy

Solution 2:

"Did you hear Eric's wedding toast? He wouldn't shut up!"

"I know, he was being a complete showboat/showoff."

Alternately, you can say:

"I know, he was being a complete grandstander."

Solution 3:

I usually like to say that..

the person likes the sound of their own voice

. It's not a one word noun or adjective but fits Eric perfectly.

Garrulous also comes close: Defintion at merriam-webster

Excessively talkative, especially on trivial matters. Given to prosy, rambling, or tedious loquacity : pointlessly or annoyingly talkative

Solution 4:

Center of attention; as in Eric always has to be the center of attention.