Tipping on good *answers* has been dealt [before](https://meta.stackexchange.com/questions/36567/how-come-no-option-to-tip-answerers), so I'm not suggesting that here. And, of course, we are able to [pass on a few rep](https://meta.stackexchange.com/questions/69103/award-a-bounty-to-a-competing-answer-on-a-relatively-uninteresting-question/71692#71692) at any time to a deserving person. Nothing wrong with that option, except that the reward isn't tied to the helpful behavior in any meaningful way; It's clear that thankful people frequently [want that association](https://meta.stackexchange.com/questions/68743/reputation-for-parent-site-through-chatting-system).

What I would like to suggest is a mechanism for directly tipping someone for being particularly helpful on a comment or in a chat room.

It would need to be:

1. Visible to *at least* the tippee where it came from
2. Cost the tipper some rep
3. An unexpected reward after the fact

I think to satisfy condition 3 it would have to be limited to a relatively small amount, so people aren't inclined to shop questions around chat offering bounties *in advance*, for instance, would be useful.