Why are there only 363 days for orphans?
Because they don't have Mothers' and Fathers' Day.
Listen up, buttercup. This joke's playing on the fact that orphans don't have moms or dads. So, they miss out on Mother's Day and Father's Day. That's two days gone, leaving them with 363. It's like saying they're missing out, see? You probably miss out on a lot too, judging by how slow you are on the uptake.