Typically used in Scotland to describe someone who participates in theatre/performing and tends to be quite obnoxious about it, also can be referred to as a 'drama wain'.
Tend to be overly excited and smiling all the time and melodramatic and attention seeking when in a negative mood.
More geared towards the ones who have been "doing it all their life" which means since they were children, hence wean / wain.
The Musical Theatre ones are the worst.
"I've done theatre all my life! I actually have rehearsals now, I'm the leading role in Fiddler on the Roof! I've also done loads of other musicals and plays and pantomimes, since I was just a baby, I was born for it!"
"You're actual such a drama wean."