Mario DID have 1000000 brothers, but they got so annoying that he killed them all! MuHAHA! But he obviously liked Luigi and only kept him alive (or Luigi went to the Groceries while MArio was on a killing spree and when he got back Mario turned over a new leaf, decided to never kill, and learn to live with Luigi).
What if you ran into Luigi while in the grocery store?
“A wagon full of pamcakes? In the Champeen ship?! I’d like to see ya try!†~ Homestar Runner