To the max, going all out, or with total energy. (The term likely refers to the 'pleno' in roulette, which is hitting a single number for the highest payout).
- How was the night? - Sick, a pleno with the music, the girls, the drinks...
A sarcastic way to describe someone who is acting like a killjoy or looks totally bored. The phrase compares the person to a pot of popping corn, which is full of movement and energy, to mock their obvious lack of spirit. (In Venezuela, gallitos is a regional word for popcorn).
Damn, Manuel, estáis más anima'o que una paila e' gallitos.