El Pollo Loco is a drugged-up fighting rooster you battle in Ramón's cave bunker during Spur of the Moment. It wears the spurs Ramón stole from Elvis Carballo, so this fight is personal.
Follow Spur of the Moment into Ramón's bunker. The rooster is waiting in the cave, and the fight starts once you reach it.
Watch its attacks, dodge them, then hit back in the gap that follows. Rushing in costs health; patience wins rooster fights.