The Myth of The Ticklish Poseidon

You know how the olympian gods are. When they're not turning into animals and chasing their mortal affairs they're casting their fury down into a poor city who failed to appease their needs. 

Unfortunately, Poseidon decided to unleash his rage on the wrong city: one protected by his sibling Zeus. The king of the gods couldn't just sit and do nothing, his brother had to be punished and turned into an example. 

Poseidon was a respected and feared god, no one could ever imagine he had a weakness so stupid like... tickling? Well, Zeus knew how ticklish the god of seas was so he commanded Hephaestos to build a special squared column which was also an aquarium, where he tricked the god and trapped him inside with an ancient octopus monster which is also a tickle deity. His feet, the most sensitive part of his body, were placed outside of the aquarium with his big toes tied and stretched in a way his feet forms a "V", like a mermaid's fin in the end of their tails, for anyone, god, demigod or visiting mortal, to play with.

Lots of deities who were angry by Poseidon's anger issues and vengeful mortals who suffered his rage took the opportunity to make it a traditional ritual to praise Zeus. During three months per year they visit the poor god, who was already being perpetually tickled by his watery "companion", and torture his soles for the glory of the king of Olympus. 

But the one who enjoyed it the most was Zeus himself. He didn't need to wait for the "Divine Tickle Ritual" and had the best tools to tickle a water deity: thunderbolts. He would shock his brother's sensitive soles whenever he wanted.

The sweat and tears the god produced inside the aquarium would overflow the amount of water and fall into the world as rain. Also, every time Zeus tickled him with thunderbolts, it caused thunderstorms and torrential rain. 

The time of the year Poseidon received his "visits" became known as "Wintickle" (later known as winter) and was the most rainy season. Many greek temples would make big tickle orgies during this time in the name of the gods. 

And, finally, that's how Poseidon became known from God Of The Seas to God Of Tickling.