Futurama (1999)

S3E2 War Is the H-Word

Fry and Bender join the military to score a discount on bubblegum. When they're deployed to battle against a planet inhabited by bouncing ball aliens, Leela decides to disguise herself as a man to enlist alongside them. Eventually, Bender is tasked with negotiating with the enemy, but it soon becomes clear that this was all part of a cunning trap.