How do you usually get rid of unwanted Humble Bundle keys?

Trade then.

give them to me lol

Giving them to me? :S
Nah, just kidding xD

I generally key drop, sometimes with a twist, or give them to someone I think deserving.

Mostly people post it in the forums so that ninjas could take them

I often give them to friends, especially with co-op games, some people like to just drop the links here in the forums :)
I don't think anyone would ever complain about you "flooding" us with keys.

Sometimes people do key drops, or just keep them to trade for games they actually want, or just give them away to others with puzzles.

I try to trade for them on steamtrades. But eventually I gave up and started a second steam account.
So I'm dumping my spare keys there and I take the cards as bonus for my main account.

use trashbot, he trades and stuff or you can just donate stuff to him

Someone got into my Humble account and used all the 20+ keys I had leftover. That'll do the trick.

Yeah, like others have said, key drops, trading for other bundle games, giveaways on here, and elsewhere, giving to friends, hell you can make your own giveaways, and use it to promote a fb page, or twitch, or whatever. Basically, you either give 'em away, or let 'em sit collecting "dust" in your HB acct. You can think a little outside the box with giveaways, and still usually get something out of it, though, lol!

They do those "flood" giveaways you are talking about, just with some CV you prefer. :)