I can understand that some German nouns (e.g. Mädchen) might just always have been whatever gender the noun is, and the explaintion is lost to the mists of time. But Bikinis were invented in the 1940s. So why is it "der Bikini"? Why is bikini a male noun in German? Surely "die Bikini" makes much more sense!
Was there some meeting where they added Bikini to the German language/dictionary, and they decided it would be a masculine noun?