Kissing Cousins / Playing With

Basic Trope: A romantic and/or sexual relationship between cousins.

Straight: Alice marries her cousin Bob.
Exaggerated:
- Only cousins are considered viable suitors for Alice—dating a non-cousin would be taboo.
- Alice marries her double cousin Bob. (Alice and Bob's mothers are sisters. Alice and Bob's fathers are brothers. They are cousins on both sides of the family.)
Downplayed:
- Bob is Alice's distant cousin, either of third degree or more.
- Alice marries her half-cousin Bob (their parents are half-siblings).
- Alice and Bob become non-blood "cousins" due to his uncle marrying her aunt; the two of them later marry each other.
- Bob is Really 700 Years Old, and a cousin to Alice's ancestor, making them cousins many times removed.
Justified:
- Alice and Bob live in a culture where cousin marriage is considered preferable.
- Alice and Bob are part of a royal family that regularly practices this for either "keeping the bloodline pure" or making sure that wealth and/or power stays within their bloodline.
- Childhood Friend Romance
- Surprise Incest
- The Squick factor isn't as bad thanks to the fact that they're cousins of a distant degree (see Downplayed #1 and #2).
Inverted: Their family practices Royal Inbreeding. Cousins Alice and Bob are supposed to marry—but they refuse.

Subverted: Someone suggests that Alice marry Bob. The idea is introduced like a valid possibility, but Alice is appalled and shuts it down right away.
Double Subverted: …because it turns out she's in love with her other cousin, Charlie. So They Do.
Parodied: Alice and Bob's grandmother is a Shipper on Deck, and serves as The Matchmaker for them.
Zig Zagged:
- Alice and Bob are cousins caught in endless Will They or Won't They?.
- They're not actually related to each other, but Alice and Bob do share a cousin in Doug (Alice is the niece of Doug's mom and Bob is the nephew of Doug's dad, or vice-versa)
Averted:
- No cousins fancy each other.
- No cousins appear at all—everyone's Conveniently an Orphan or the Last of His Kind.
Enforced: The author wanted to include Brother–Sister Incest, but that was Bowdlerised to cousins.
Lampshaded:
Dana: I'm going to my cousins' wedding.
Eva: You mean your cousin's wedding.
Dana: No. I mean my cousins' wedding.

Invoked: Their grandma wants to see all her grandchildren married before she dies. Why not kill two birds with one stone and get two grandchildren married at once?
Exploited: ???
Defied: Bob refuses to marry his cousin Alice.
Implied: Incest Subtext
Discussed: "Oh, come on, we're like a zillion times removed! Why is everyone making this a thing?"
Conversed: "Alice and Bob is one of those old books, where everyone marries their cousins, you know?"
Deconstructed: They have a kid, and the kid has a certain genetic disease that runs in their family.
Reconstructed: They both have experience with this disease, considering it runs in their family, and they are very well-equipped to handle their child's special needs.
Played For Laughs: Alice and Bob are part of a crazy, royal/wealthy family and its treated like a throwaway joke.
Played For Drama: Alice and relationship with Bob, as cousins, is no different than Alice's relationship with Charlie, who's the son of her Honorary Uncle. She's childhood friends, family friends, with both of them. Alice and Charlie date for a while, before becoming Amicable Exes. Then Alice and Bob fall in love. Everyone is horrified and outraged by this, while no one batted an eye at her relationship with Charlie. Alice can't understand why one Childhood Friend Romance is ok, while the other is not—they only share an eighth of their genes.