Frick and Frack

Frick and Frack

Two very close friends. "Frick and Frack" were two characters in the Ice Follies starting in the 1930s. Katie and Molly have always been like Frick and Frack, so I'm not surprised they're going to the same college now too.
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Farlex Dictionary of Idioms.

Frick and Frack

Two inseparable and indistinguishable companions. Frick and Frack was a Swiss comedy ice skating duo who appeared in the original Ice Follies, starring in the late 1930s show as comedy ice skaters. Dressed in identical alpine lederhosen, they astonished audiences with extraordinary feats of athleticism. Thereafter, any two guys who palled around together, especially if they were of the same build, were called “Frick and Frack.” And since enough such pairs were considered cutups, “Frick and Frack” also came to mean two jokesters, the way a trio of town clowns was the Three Stooges.
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Endangered Phrases by Steven D. Price
See also:
  • battle of the giants
  • Box and Cox
  • between two fires
  • come together
  • at each other's throats
  • chalk and cheese
  • be at each other's throats
  • (one, two, three) strikes against (someone or something)
  • cling together
  • in two
References in periodicals archive
Capone and Nitti, Abbott and Costello, Frick and Frack ...
Only a few weeks after signing a new contract with KFYI, Goyette was replaced in his coveted drive-time slot with a duo he describes as "the Frick and Frack of Bushophiles, two giggling guys who think everything our tongue-tied president does is 'Most excellent, dude!' I have been relegated to the later 7-10 p.m.