Shortstack walks in office with a stuffed tortoise from one of the Kohl’s Cares for Kids sets that came out a while back. The tortoise’s legs are covering his eyes.
‘Look, Mom! He can’t see. He’s been blonded!’

So it turns out that the ‘tighties‘ Shortstack was referring to weren’t tightey-whiteys after all, rather tights/pantyhose/stockings, etc. It clicked as we were changing from our school/work clothes to our ‘we aren’t doing SQUAT this afternoon’ attire and he saw the fist sized hole I had poked through the support pantyhose I wore [...]

Shortstack has always asked for ‘piggy bank’ rides, as opposed to the usual ‘piggy BACK’ ride. Clever, astute analysis of this particular choice of words escapes me; thus I open the floor to you clever, astute Internet folk!

The king of random conversation, Shortstack breaks the short silence while we were driving today.
‘Mom, why do you always wear tighties?’
You are correct, tighties as in ‘tightey-whiteys‘.

according to Merriam-Webster online:
‘the condition of having one’s clothing wedged between the buttocks especially from having one’s pants or underpants yanked up from behind as a prank — often used with get or give’
I much prefer Shortstack’s choice of words:
‘my bottom is sucking up my underwear’