Ever had a flying burrito hit you? Well, it's a deadly projectile, right up there with cannonballs and grenades.

This quote is suggesting that burritos can be a dangerous weapon when thrown. It suggests that if you get hit by a flying burrito it can be just as dangerous as if you were hit by a cannonball or a grenade. In other words, burritos can be dangerous if used as weapons and should be treated with caution.