Online. BTC was made for it. Scan QR tap confirm and done.

I don't have cellular service. I refuse to pay a phone carrier so they can track me via a SIM card. I loathe being interrupted by spam calls too.

So for someone like me who dosen't have internet on the go, its really hard to pay with BTC in person. IMO, handing someone a piece of paper to settle txns IRL will always be the simplest.