Spit Shake

Two people who have just come to some sort of agreement both spit in their palm and then shake hands with the wet hand.

Basically, this is the "lite" version of a Blood Oath. However, it still conveys utter seriousness that is many steps above a Pinky Swear. Plus, it avoids the horrors of showing an actual Blood Oath. And finally, it happens in real life, so it's hardly unrealistic. It's often used by children, country "bumpkins" (who are probably not as simple as they are assumed to be by the other party to the agreement) or members of certain cultures, like Roma and Irish Travellers.

A popular comedy trope is to have the resident Neat Freak act disgusted or shocked at having to do this in order to seal a deal.

Not to be confused with Spit Take.

Examples of Spit Shake include:

Fan Works

Applejack tries to seal a deal with Phoenix like this in Turnabout Storm. He passes.

Phoenix: I'm not touching that hoof.
Applejack: *sigh* You are just as prissy as Rarity!

Film

Happens in Free Willy 2 between Jessie and a female friend, then later, an adult who helps him out.
David is originally repulsed by the idea of a spit handshake at the beginning of Newsies, but he comes around by the end.

Literature

Happens in Pyrates, twice. First when the three main friends agree to work together to search for the treasure, then again when a new kid joins.
Discworld:
- Happens in The Truth. One of the homeless tries to Spit Shake with the dwarf running the printing press. Deword stops him with "Do you have any disfiguring diseases? Do you want some?"
- In Making Money, Moist does this when arranging a bank loan for Harry King.

Harry: I didn't think bankers did that!
Moist: They don't often shake hands with Harry King, then.

Also referenced in the novel To Kill a Mockingbird. The teacher Miss Caroline asks Scout to hold out her hand (intending to hit her with a ruler as punishment), and Scout wonders to herself "what bargain [they] had made" as she thought "she was going to spit in it, which was the only reason anybody in Maycomb held out his hand: it was a time-honored method of sealing oral contracts". Is referenced again in the following chapter during a scene with her father, Atticus.
Pops up twice in the first Sparhawk series. First when the Loveable Rogue Platime - head of the local Thieves' Guild - is recruited to join Queen Elahna's council as an adviser. Platime, being a commoner to the last hair, seals the deal with a spit-shake, and Queen Elahana follows suit, if only because she was in the middle of tricking him into accepting a really clever 'bargain', and didn't want to get distracted. She only admits to being grossed out by it afterwards, when she demands a washing-basin IMMEDIATELY so she can wash her hands.
- Quite a bit later, she uses a spit-shake to seal a deal with the newly-named Archprelate - he needs a ring passed down through the royal family of Elenia for generations, in order to launch a desperate mission to stop the evil Zemochs - and Elahna wants to marry her beloved (but quite a bit older) knight, Sparhawk. The Archprelate agrees to the bargain, and being a clever old fellow who's been around the block a few times, he recognizes the spit-shake gesture and follows through. Sparhawk is somewhat distraught by seeing his life get traded away like that.
One happens between Tuon and Mat in The Wheel of Time. Oddly, despite Tuon being royalty, she really doesn't mind.

Tabletop Games

Paranoia supplement Acute Paranoia, adventure "Me and My shadow Mark IV". After the PCs finish guarding Markie, the Computer orders them to spit on their palms and shake hands with the R&D representative as part of the transfer procedure.

Western Animation

Was used in Peter Pan 2: Return To Neverland, when Peter Pan and the Lost Boys used this as their group handshake. Jane at first shows her disgust at it, but ends up participating in it herself later in the movie.
On The Simpsons, Bart and Milhouse do it to be "spit brothers" when the Simpsons have to move away.
Rita and Roddy on Flushed Away. City Mouse Roddy has to be reminded to spit in his own hand.
In My Little Pony Friendship Is Magic, Applejack and Rainbow Dash do this throughout "Fall Weather Friends". Applejack attempts one with Rarity in "Look Before You Sleep", but Rarity is disgusted by it and doesn't go through with it.
- The "shake" part is a little different as well, since they're ponies, and as such, don't have hands. What they do is push their hooves together in what the fandom calls a "brohoof" (so named because it greatly resembles the "brofist").
Done by Jimmy and Beezy on Jimmy Two-Shoes.