How do you deal with a champ who keeps popping your barrels as GP?

Stop sucking.

get them first? it's a minigame, you gotta win it

Depends on the situation. If you're fighting a ranged champion that build attack speed: you're (in my experience) wasting your time. Their auto attacks are faster and have further reach.

Against a Mage or just ranged autos, I'd find a way to obscure the first barrel (like put it in a push) and wait. When they are in a spot you want, put a barrel there (it has to connect with the other barrel) and immediately shoot the first.

GP's barrels take practice. Though at one point you may be good enough to trigger it during the second tick (at 3rd ult rank the timer is a lot faster. Usually firing it after half the second tick will trigger the boom when you consider your missle speed).

They're also devastating in knock up comps. By Max ult rank, one barrel will be at one tick by the time the enemy team comes back down from a Malphite or Braum ult.

The same way any melee champ deals with Gangplank: Being completely impotent and trying not to die.

if they are going out of their way to kill barrels, try putting one down to bait for a gank. sometimes i just dont use them much.

too bad... i hate your barrel... use cheap strategy is the worst!

A couple thoughts. odds are its ranged champions giving you this problem. GP is slightly countered by ranged champions since they can do just that while avoiding being in the zones of the barrels. Thus my first answer would be not to pick GP into a ranged champ if you can avoid it. Second, utilize the brush in lane. Place a barrel in a bush, let the wave push towards you, then you are more likely I succeed in barrel chaining.

One of the more difficult mechanics of GP is the need to have quick barrel mechanics to be able to time everything correctly to have one barrel down and ticking to zero, throw another barrel at the feet of the enemy and parrley the first barrel all in about 1-1.5 seconds. It can be tough but that's the main combo

im that guy that usually consta-destroys barrels and what works on me is when i go to auto attack one, gp throws another directly under me and shoots either. Tends to work pretty well

Shoot them in the face instead.