This term is considered to be foul language in most social situations and you should not say this in conversation. It is a bad habit to start.

'af' is short for 'as fuck' So it means somebody is 'bored as fuck' which just means somebody is really bored. It is used online, in conversation a person would never say 'I'm bored af'

On the internet people sometimes write "af", where it's short for "as fuck".

"Bored af" means extremely bored. This is shorthand for "bored as fuck". "As fuck" is a colloquialism that denotes that something is to an extreme degree. i.e. He is dumb af. (He is incredibly stupid.) They are gullible af. (They are extremely gullible/ They are fooled quite easily.) I would not recommend the use of this adverb in formal conversations.

It means as fuck