it can have a bunch of different meanings—
as a situation (usually a particularly ridiculous one)
an adjective, either to describe a friend that’s silly or unordinary or a significant other that’s very dear to one’s heart but also shares that silliness
this could be used in any case, depending on the context.
situation:
A: What are you guys arguing about?
S: She won’t remember a song I added to a playlist!
A: Imagine having a shimwaggle about this!
friend:
A: You’re such a silly shimwaggle!
J: Awh, thanks.
lover:
J: He’s my little shimwaggle. 💓
A: Cute!