Reading a few more stories unearthed another memory that could qualify, except we (H and I) were on our way to visit parents rather than on vacation. We were fairly newly married and quite poor, so we stopped in the cheapest motel we could find in VA (lived in FL, heading to NY). We were both asleep when a man put his key in the lock, opened our door, and walked in - thoroughly surprised to see the room occupied. We were as surprised to see him. H insisted we get up, get a refund and leave. The head office told him we must not have locked our room, but H knows we did - he didn’t like the setting of the motel anyway and double checked.
Gives another meaning to a “double room,” which is now how we describe it when reminiscing.