Green’s Dictionary of Slang

(Irish) angry, keen.

1901		‘Miles Franklin’ My Brilliant Career 170: Joe Archer said he was ‘leppin’’ to begin, so we adjourned to the dancing room and commenced operations.
c.1940–5		‘Myles na gCopaleen’ Best of Myles (1968) 151: defendant (addressing court): Yez are all leppin’ because I didn’t skip.