If you’re wondering when International Mixed-handedness Day is, it, like ambidextrous people, doesn’t exist. If you pitch southpaw, then it doesn’t matter if you catch southpaw, too. You’re left-handed. (And let’s not get into the affront to god and threat to right-handedness that trans-handed people present.)
So, if you know a left-handed person, pat them on the back — with your correct hand. Tolerance is really in right now.