Good question. Snakes, by themselves, are not angry if that is what the "mad" means.
It still doesn't work if the "mad" means crazy or whirling around not knowing what to do.
mad as swarming bees
mad as hornets
crazy as a loon
mad as bats
mad as a basket of snakes
("All" can be a singlar/collective or plural noun)
Student or Learner