Fool for Love

"I may be love's bitch, but at least I'm man enough to admit it."

—Spike, Lover's Walk

"The things I do for love."

—Jaime Lannister, A Game of Thrones, before throwing a little boy off of the top of a tower

You've got yourself a Badass snarker who couldn't care less about anyone. Or could they? Maybe this supreme example of all things awesome is hiding something, some hidden feelings. Maybe they are just a big softy inside.

Then we have ourselves the Fool for Love. He may act all macho, but his bravado is really just hiding the fact that his one motivation is to honor his one true love. Given enough time and enough drama, this one true love may even turn out to not be so one and true. Even in this case, the Fool For Love will almost immediately move on to a different love interest and serve them as loyally. All while being the most obnoxious character in the ensemble.

Often, but not always, the Fool for Love has a secret artsy side. He may seem like a gun (or sword or fist) slinging showboat, but when no one is looking he is reading and writing poetry. Or painting landscapes. Or just looking forlornly at the horizon, but real artfully.

The quintessential example would be Spike from Buffy the Vampire Slayer and later Angel. He may be the biggest Badass on the show (at least in the show's first few seasons) but he is always doing it for a very special lady, whether she be a psychotic vampire, a troubled slayer, a cute physicist or an elder goddess. He snarks and acts all tough but at the end of the day, all he wants is to watch out for his one true love.

Examples of Fool for Love include:

Anime & Manga

Sanji from One Piece is a self-confessed Slave to Love. Any moderately attractive woman can manipulate his chivalry, and any woman period is subject to his protection. Even if they're enemies.
Harima Kenji from School Rumble fits the badass-in-love description to a T in his feelings toward Tsukamoto Tenma.
A (maybe) platonic version of this is Kamina from Tengen Toppa Gurren Lagann initially appears to be a big, boastful, fearless meathead, but his bluster is both a cover for his inner doubts and a way to inspire courage in others, especially his Blood Brothers Simon. He admits to Yoko in episode 8 that he'd have given into despair long ago if it were not for his absolute faith in Simon, and shortly thereafter goes on his first mission where he and Simon fight separately...and only Simon comes back alive.
The typically caustic Chazz/Jun from Yu-Gi-Oh! GX always goes crazy in the presence of Alexis/Asuka and always tries to impress her, but always fails.

Comic Books

Wolverine sure seems like an uncaring loner until you look at the gaggle of one true loves he has loved and lost throughout the years.

Literature

Riley Biers from Eclipse, who did everything in the name of his lover, Victoria. He was only a pawn to her.
Jamie Lannister in A Game of Thrones. He may be the deadliest and most sarcastic knight in the Seven Kingdoms, but everything he's done he did for his special somone.

Live Action TV

Spike, from Buffy as described above
Sawyer from Lost definitely qualifies as one of these. He may be a rugged con man who insults anyone who will stand still long enough but his only two hobbies are reading and gazing forlornly at Kate.
- At least until Season 6, when he takes up listening to punk music and mourning Juliet.
Damon from Vampire Diaries is definitely one of these, in the same vein as another snarky vampire. He spends 146 years searching for Katherine and falls for her doppleganger, Elena to whom he is just as loyal to, if in his own crazy way.
Simon from The Inbetweeners will do anything for the girl he happens to be in love with at the time. Him being one of the main characters and thus one of the universe's playthings, this usually ends badly for him.