celebration by proxy

Something one does to treat themselves, due to a celebration going on for someone they are close with.

“It’s my roommate’s birthday tomorrow, so I’m having a cheat day as my celebration by proxy.”

PNIUS

Pun Not Intended Until Said
(pronunciation is still tbd)

Elastigirl: Last night was incredible!
Mr. Incredible: PNIUS?
Elastigirl: PNIUS.