a person, usually a guy but not limited to them that for whatever reason doesn't want other people to be successful, usually with girls but not limited to them and therefore, hates on you.
1.) you could be at a bar talking to the best looking girl in the joint, and this girl might be all about you too, but then your drunk buddy who happens to be a hater rolls up on the scene and starts falling all over the place, making you look like an asshole and scaring her away. That's a hater.
2.) you might be in a bedroom with a girl about to get a piece and then all of the sudden, your buddy starts banging away at the door for no reason. He just wants to figure out a way for it be as hard as possible for you to get some. That's a hater.
3.) the worst kind of hater though is the one who talks bad about whatever it is you're doing, but only when he's not involved himself. when he's part of it, it's all good, but when he's not doing what you're doing, don't be surprised if he's talking bad about it to everybody else.
something you say to somebody when you don't really give a shit about their story. this is a phrase usually used when somebody else won't shut the fuck up about something you don't give a fuck about. you usually let them talk for a little while but when they get to the point of being annoying, that's when you tell them, "Say I swear to God." In short, it's just another way to let somebody else know you don't care. When you tell them to say "I swear to God," they usually get the message right away after saying "I swear to God," and shortly afterwards realizing that it means you don't care.
Melissa: Cancun was so awesome! We were at the bar every night! We met totally hot guys! One night we all danced on the bar after we did like, 20 jelly shots apiece! And then Jill made out with some guy who was like, 35 years old! We were all dying laughing! It was so funny!
Me: No way! Say I swear to God! (in a cocky ass, sarcastic manner)
Melissa: I swear to God! (realizing you don't care)