Day 1ish is PG slang for "Day 1 shit" which is often used to get around using curse words or the word 'shit' on broadcast TV.

Day 1ish means that you've been doing your thing since the beginning -- or Day 1.

Day 1ish was founded by the Uso twins on WWE.
I've been ride or die with you since Day 1. That's Day 1ish.
by dabecka August 29, 2023
Get the Day 1ish mug.