Leave a comment, then delete it after you're confident the recipient will have seen it. (A few hours or days depending on activity.) You and they get to feel go

Leave a comment, then delete it after you're confident the recipient will have seen it. (A few hours or days depending on activity.) You and they get to feel good, but the clutter isn't left around for other users. This is what I often do. It is a tolerated behaviour, even if some people aren't thrilled with it.