odd man out

n., pl., odd men out.
One who, because of strangeness of behavior or belief, stands alone in or out from a group.

1.  A person who is left out of a group for some reason, as in The invitation was for couples only, so Jane was odd man out. [Mid-1800s]
2.  Something or someone who differs markedly from the others in a group, as in Among all those ranch-style houses, their Victorian was odd man out. [Late 1800s]

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The noun has one meaning:

Meaning #1: someone regarded as eccentric or crazy and standing out from a group
  Synonyms: kook, odd fellow, odd fish, queer bird, queer duck

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