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ants in one's pants, have

Idioms  
  1. Be extremely restless, uneasy, impatient, or anxious, as in This child just can't sit still; she must have ants in her pants . This rhyming idiom calls up a vivid image of what might cause one to be jumpy. [ Slang ; 1920s]

  2. Be eager for sexual activity, as in Bill's got ants in his pants for Rita . This usage is less common today. [ Slang ; 1920s]