Defined by having two "opposite" characteristics in a friendship.
The persons becomes your good friend one day but becomes an acquaintance the very next.
The pattern of "Good friend to acquaintance" and vice-versa continues, often gaping from days to weeks, to even months.
Iqra: I met Khaqan at a party and we became very good friends, however we didn't talk much at all after the party ended, but recently, we ran into each other on the street and hung out like we were very good friends. I don't know what to call this friendship.

Muhammad: You two are Bipolar friends.
by ikrasaleemkhan March 11, 2013
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Usually a girl (sometimes men) who one minute are so mad about something one of their friends did and then 5 seconds later they are smiling and laughing about the same thing that made them mad.
Oh my god why didn't you tell me to turn left here?! What the hell! Oh how silly of me I didn't turn left, I'm such a bipolar friend
by CandyVentura July 8, 2011
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A friend who will hang out with you, and you will genuinely get along with, but when they're given the chance to gain some popularity will suddenly not be your friend anymore. may even bully you if necessary.
bipolar friend: "HEY! what's up? how've you been??"

Normal friend: "Not much, how about you?"

(another person walks by, presumably popular)

bipolar friend: "Uh, i don't know, why they hell are you talking to me? dumb ass.

Normal friend: "Your such a bipolar friend. go f**k yourself."
by Feely7 February 13, 2011
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When your friend says they want to go to a party but then change their mind 5 minutes later and then change their mind yet again another 5 minutes later and then they're stuck in this endless loop of deciding whether or not to go.
Jill: Okay! I'll go to the party!
*Some time passes.*
Jill: I don't want to goooo!
Anthony: Wow, you bitch.
Luke: At least we know the bipolar friend of the group.
by DefineShitMan April 11, 2019
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