What is Ants In Your Pants?
1.
To be nervous or anxious or jumpy; to be unable to sit still.
If you had 'ants' (small insects) in your 'pants' (clothing) you would probably feel like jumping around.
Synonym:
1) The children had ants in their pants, so we took them outside for some exercise.
2) Would you please stop tapping your foot?! You must have ants in your pants!