When he’s, it’s, etc. at home
Definition 1 of 1
Pro Tip 1/3Joking Tone
Used humorously to express skepticism or imply the subject is obscure, bizarre, or unfamiliar. 
He's an expert in cryptobiology, whatever that is when it's at home.
Pro Tip 2/3Light Sarcasm
Implies playful sarcasm or irony, signaling you find what's mentioned odd or questionable. 
So you're a digital prophet now? What's that when it's at home?
Pro Tip 3/3Colloquial Usage
It's informal and best used in casual conversation, not in formal or written contexts. 
She says she's a mixologist, whatever that is when it’s at home.