Someone who you have sex with without actually being friends with that person or being in a girlfriend-boyfriend relationship. Just for sex. Two people who have sex. Sex. Only sex. Together just for sex. Sex! Emphasis on sex and nothing else. Se-uh-uh-uh-uh-uh-kz!!!! Sex!!!!!!!!!!!!!!!!!!!!!!!
Sexfriends only do one thing together. Sex!

When you eat dirt for the first time and leave your family to build a shack in the woods

A friend you have sex with (d'oh) but without having a romantic relationship.

Same as fuck friend or bonk buddy.

A person you do, cose you aint getting it from someone you love.

Adjective

A step above a hookup but below friends with benefits

Normally followed post coitus with a high-five

A couple (if you can even call it a real relationship) who's only real redeeming quality is to fuck each other. These "couples" often soon break up shortly after meeting. The female loses interest as she expects to be brutally fucked every night. These "couples" often tend to ignore family members, do drugs (not always but very common upon the culture), heavy music (loud music that has no fucking value what so ever).

A sex friend usually leaves quickly and is a bad thing to see in a relationship.