They're referring to the tags on your user name's posts.

For example, you are currently tagged as "Member" Shelby is a "Junior Member" While I'm a "Senior Member" (To the left of your avatar)

Lenny is a Sup moderator so he has the tag "Supreme Moderator"

Anyone who is banned either has the tag "Temp ban" or "Banned"

So the in-law tag was really just sarcasm (I'm guessing) and mildly funny.