"expert, connoisseur," by 1965, from Yiddish meyvn, from Hebrew mebhin, literally "one who understands." Plural is mayvinim.
"piercing that consists of a ring which goes through the urethra and out behind the glans," mid-20c., supposedly so-called from the modern legend that Albert of Saxe-Coburg-Gotha (1819-1861), prince consort of Queen Victoria, had one.
But the term seems to be not older than bodyart maven Doug Malloy and his circle, and the stories about the prince may be fantastical inventions, perhaps to explain the term. Perhaps, too, there is some connection with Albert underworld/pawnshop slang for "gold watch-chain" (1861), which probably is from the common portraits of the prince in which he is shown with a conspicuous gold watch chain. Many fashions in male dress made popular by him bore his name late 19c.