A person who is constantly making people's lives worse. There are many ways in which one can do this. That person is usually very annoying, a pussy when it comes to doing anything moderately badass, always exaggerates whatever effects mind altering substances have, will take things from you saying they will pay you back but never will, always bum other peoples things (food, gas, weed, alcohol), only wants to be your friend because of things you have that the person wants, etc. This term also goes hand in hand with hotboys, because most fuckboys are hotboys as well. (see hotboy)
friend: Yo dude sidon asked me to match him on this blunt
you: Cool how was it?
friend: When I got there, he said he smoked his weed and asked if I would throw down this time.
you: So did you?
friend: Yeah, he said he'll pay me back
you: Damn dude, you're dumb he's never gunna pay you back
friend: Why not?
you: Cuz dude, he's a straight fuckboy