Playing Pirates is the fifth stage in Swimming Cats.
This level is quite easy. A deluge of anti-red cats will work just fine. Axe cat, Swordsman Cat, Viking Cat (Rare Cat), it doesn't really matter, they are all good. Just spam meatshields and keep on pounding away with your cats.
If you are having trouble, try getting 100% gold treasures on Empire of Cats stages to improve your stats.
NOTE: Sexy Legs attacks slightly faster than Gross does. Same goes for Dragon and Lizard.