[quote=@SentientOne]
<Snipped quote by Silly>

a [i]WHAT[/i] now??
[/quote]

Where someone basically makes their character "them" or an idealised version of them. 

Usually overly attached to their character, where it impedes roleplay and an IC slight is taken as an OOC insult and associated drama is what they are known for.

TV tropes link: https://tvtropes.org/pmwiki/pmwiki.php/Main/SelfInsertFic