Shirt a girl wears that belong to her boyfriend and therefore most likely 10x larger than her body size. May also stink with sweat or possess an overpowering smell of cologne depending on her boyfriend's hygiene.
"나은 had been wearing that boyfriend shirt everywhere for 3 months now... to the bus, her workplace, and even to the mall. She should probably wash it already."
by 이태민 February 16, 2014
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A boyfriend shirt is historically an oxford style shirt taken from a man’s closet by his girlfriend without his permission and worn around his apartment or house, generally with nothing on underneath. This usually occurs the morning after they spent the night together.
I looked into my boyfriend’s closet and found a shirt to wear that became my boyfriend shirt.
by Leap Cruncher October 07, 2021
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This may also refer to girls: Boyfriend Shirt Syndrome (BBS) occurs when you see your girlfriend/boyfriend/significant other wearing one of your shirts or hoodies and you either a) just find it completely adorable or b) find it sexually appealing, which it is more often found in the latter and referred to as "Boyfriend Shirt Syndrome". Though it is typically known with mainly shirts and hoodies, it can refer to any artifact of clothing.
Sandy: What is BBS?

Miranda: BBS? Oh "Boyfriend Shirt Syndrome" could be defined as when you see your girlfriend/boyfriend/significant other wearing one of your shirts or hoodies and you either a) just find it completely adorable or b) find it sexually appealing, which it is more often found in the latter and referred to as "Boyfriend Shirt Syndrome". Though it is typically known with mainly shirts and hoodies, it can refer to any artifact of clothing.

Sandy: OHHH
by Raven Nevermore January 25, 2017
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