One might think they are pinged after a few swigs of a drink, not because the alcohol is actually affecting their brain, but because they think they should be feeling something already. This is a placebo effect, and causes people to loosen up for no apparent reason and others to call them lightweights.
Pinged is often the only state where one can be confident they are below the drink-drive limit.
Dweezil: Just two beers, I'm still cool to drive.
Bob: You sure? You're not even buzzed yet?
Dweezil: Nah, just pinged.