You know, there isn't really anything wrong with this guy. He just doesn't measure up for some reason. Somebody else can make the jokes he tells a little funnier. He could use a little help in the wardrobe department. He loses a lot of women to the taller, more handsome, more suave guys (and/or the bad-boy types). Or, maybe he has all of those qualities, yet somehow isn't quite Mister Right Enough for the leading lady, who prefers the Protagonist's flaws.
The reason this character shows up so often in stories is likely to make a statement about the mysterious ways of love and about how the chemistry between two people is something that cannot be predicted. This message is a little undercut by the fact that certain people seem to be exactly the type to be cast as second-runner in a romance. Perhaps the chemistry is not so mysterious, after all.
Note that although this trope largely applies to male characters, it can occasionally affect female characters as well, particularly in Love Triangle relationships where there're two women and one man. In these cases, the exemplar of this trope is usually the "Betty" of a Betty and Veronica matchup.
Sometimes called "The Baxter" (but not Ted Baxter) from C.C. Baxter of The Apartment, a sad sack who actually gets the girl. The Michael Showalter movie The Baxter deconstructs the concept. Compare Hopeless Suitor, Romantic False Lead, Unrequited Tragic Maiden, and No Sparks. See also Did Not Get the Girl and Everything but the Girl when it's The Protagonist who is the romantic runner-up.
Note that since this trope involves the resolution of love triangles, SPOILERS AHEAD!
Please don't use this trope to bash Official Couples that you don't like, too.
- Proteus in Sinbad: Legend of the Seven Seas.
- The narrator of "I'll Be Around" by The Spinners.
- Matt Hardy and Daniel Bryan share the humiliation of each having lost a romantic rivalry to Kane. That's right, Kane - a socially awkward, genuinely ugly, supremely sadistic borderline Humanoid Abomination. Then again, there was a saving grace in each case in that the girl in question proved to be a total slut.
- Dandelion: Heejung never seems to consider her college friend Heejae as a potential romantic option. In fact, he only confesses his feelings to her if the player failed to properly romance any of the other guys, making it a Bad Ending.
- Kain from Final Fantasy IV.
- In Mass Effect, Dr. Michel has feelings for Garrus but will lose to a female Shepard who romanced Garrus in the second game, and even if the player does not romance him, he'll end up with Tali if Shepard didn't romance her.
- Given the many ways one can play their character, almost all of the series' party members can be subjected to this if Shepard decides to romance one character in either of the first two games and end up with someone else in Mass Effect 3.
- Erfworld has Jillian, who has three people in love with her. After she leaves two behind to go after the third, one of them asks the other why he didn't go with her.
Jack Snipe: Hm, well... Could I ask the same of you, then, [Wanda]? Could it be the same answer? I mean, I wouldn't have minded so much counting myself among Queen Jillian's trophies. But I wouldn't much have enjoyed placing, oh...thirdish among them. I would say she left with the one she really came to take. It seems there is Ansom, and then there are ancillaries. And where is the glory in being a spare?
- In El Goonish Shive, both Susan and Diane end up as this when Elliot starts dating Ashley.
- In Punch an' Pie, Heather's mother describes Heather's ex-boyfriend as squarely fitting into this trope (he hasn't been seen, though). Angela's ex-boyfriend from the prequel had a lot of these traits but doesn't quite fit the trope.
- Cooper from Ben 10. In Alien Force, he shows himself as a caring, humble, and really intelligent kid who has a deep crush on Gwen. However, she never showed any interest in him (she even tried to avoid him many times) and always chose Kevin over him every time he appeared. This trope was taken to the extreme in Ultimate Alien during the first season finale. Cooper had a fast growth and became a big teenager who was pretty much a palette swap of Kevin (only blonde). He worked hard to make sure Gwen's plan of stopping Kevin was a success and even defended her when Kevin almost killed her, yet all he got in the end was a thank you and a kiss on the cheek from Gwen, followed by seeing her giving Kevin a big kiss on the lips.
- Cupid from Ever After High seems to be headed this way. Dexter is oblivious to her crush on him, probably because he's too head over heels for Raven to notice. Raven reciprocates the feelings, and while they aren't official yet, all signs seem to be pointing in that direction.
- In Gargoyles, Brooklyn has some bad luck. First he fell for Maggie (mistaking her for a female gargoyle at a time when they believed Demona was the only one left), but she was freaked out by him and ultimately wound up with Derek/Talon. Then he's clearly depressed when Angela chooses Broadway over him (Lexington having bowed out of the cock fight for some reason). Word of God and the official comic continuation eventually throw him a bone, however, when he meets and marries Katana.
- The Legend of Korra:
- Mako. While he did fumble up his relationships with Korra and Asami a lot over the first two seasons, one could argue that in Book Four, he was mature enough to finally hold a relationship. In the end, however, he ends up as a good friend to both Korra AND Asami. He's also the runner-up to both as the two, in the Grand Finale, have a Relationship Upgrade.
- For some delicious irony Korra and Asami are able to bond and become closer over their shared bad experiences with dating Mako.
- Blythe Baxter from Littlest Pet Shop (2012) had Josh Sharp falling into her arms as he swoons with her, even though he loses her each time she leaves him, hoping to go back to her room, resulting in a major heartbreak, due to the song Keep on Loving You by The Donnas.
- Miraculous Ladybug: In Kagami's Season 3 résumé, she was specifically designated as an obstacle between Marinette and Adrien; that season ends with the two dating Luka and Kagami, respectively, only for Season 4 to immediately break both pairings up. From that point on, both barely appear beyond occasionally acting as Sixth Ranger part-time heroes... or, ironically, acting as Shippers On Deck for their exes.
- Tom in Star vs. the Forces of Evil. He spends most of seasons 3 and 4 (ie nearly half the series) as Star's boyfriend, but they break up right as final story arc begins. 5 episodes later (and less than a day in-universe), Star and Marco become a couple and remain together through the finale, even bringing about the ending via The Power of Love.
- Pearl in Steven Universe was in love with Rose Quartz AKA Pink Diamond for thousands of years and was her right hand during the war for Earth. When they settled on earth permanently, Rose would sometimes date humans but Pearl never truly paid much attention as Rose would inevitably outlive them due to gems being effectively immortal. Everything changed when Greg Universe came along and they fostered a relationship deeper than any other Rose had had before. Ultimately, Rose chose Greg and gave up her physical form to bring Steven into the world. Pearl would become one of Steven's caretakers from then on but still pined for Rose and her relationship with Greg remained tense up until "Mr. Greg" where the two reconciled after her song "It's Over Isn't It"
Pearl: You won and she chose you...and she she loved you and she's gone...it's over isn't it... why can't I move on?