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 _______"
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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
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
Grandstander or failing that, any of the synonyms posted here