Grouchy snailitis is a snail disease caused by a splinter. It is only seen in the episode "Once Bitten." It is an infection that causes mild symptoms similar to the real life Rabies Virus caused by extreme pain. Supposedly, after Gary bit Squidward Tentacles, Grouchy Snailitis appears to mutate even further into Mad Snail Disease. A highly contagious disease which causes the same symptoms but in other sea creatures. After Gary goes on a rampage and bites several other Bikini Bottomites, he supposedly started an 'outbreak' of MSD and the 'infected' began rampaging across the Bikini Bottom.
It is a disease caused by a splinter pricking part of a snail's skin. It can be diagnosed by an S.D.E. or S.E. expert, such as Dr. Gill Gilliam. It seems that it is further caused when snails are in extreme pain. Symptoms are rabies-like, the infected snail becomes full of rage and foams out of the mouth. The veins in their eyes bulge and they react violently to touch.
Role in episodeIt is only seen in the episode "Once Bitten." In the episode, Gary contracts the disease, causing a rampage of him around town, biting people with a supposed "mad snail disease." It is revealed later in the episode that Gary only has grouchy snailitis. With the hoax of MSD revealed, order returns to Bikini Bottom.
It has only been identified in Gary. It was diagnosed by Dr. Gill Gilliam, SDE, SE. It can only infect snails and is not virally contagious.