It means to happily show off , or be proud of your achievements. The word is a slang common among the Lagosians, in Nigeria, West Africa. It is derived from the Yoruba word "buga"
Buga is an animal who always asks for money in public places, steals food and thinks he's cool by riding a pathetic gay ass BMX. In some cultures he is considered the god of cringeness and pure stupidity. You can identify a Buga by he's signature line :"mami".(warrning! extremely dangerous individual, don't gat close, it's contagious)
buga:"hey, mami, u wannasee some tricks?"
girl:"oh fk... a buga."