I will keep it as simple as I can. These are skin ideas that just occur to me. Sometimes they just pop out when I am working in my orchard, or when I play the game itself or when doing something. Here goes:
Golf Player Jarvan IV
He would be dressed like this http://www.scavengeinc.com/images/Product/medium/rasta/old-tyme-golfer-costume.jpg Instead of his spear he would wear a golf club.
Whenever his innate activates he would swing his golf club like all golfers do. His flag would be a golf hole flag that he can launch as his ordinary flag, and of course on the flag instead of number would be his face.
When executing his ultimate he would jump in air, saying: FORE!!!! Instead of dirt, the cataclysm ring would be composed of sand and whenever he hits someone inside the ring a cloud of sand would go up in air.
Tennis Player Darius
Instead of his axe he would have a giant racquet. Whenever he hits his opponent instead of: SHIIIIK, SHOOK you would hear a loud POP! Same as the tennis player hits the ball.
He would have a standard tennis garments, white t-shirt, white shorts and white shoes along with rainbow collored head band.
Instead of blood drop as his passive, a small tennis balls would hover around player.
He would look similar to this http://th09.deviantart.net/fs71/PRE/i/2012/100/5/8/safari_hunter_by_spider_loot-d4vqk84.jpg
Instead of keeping his cowboy voice, a new voice could be inroduced. Same as nobles of England from earlier centuries.
This skin idea was inspired by an anime show http://3.bp.blogspot.com/-LV4STRlm6d0/UCFjjQozR4I/AAAAAAAAAPg/vhtpxvNb1iY/s1600/berserk+02.jpg and I think it could fit Garen as well. I suggested this idea several times here and I think it is worth mentioning it again.
As Garen wields the same big sword as Guts and they both can charge in with all their might ignoring enemies on the way.
This skin is inspired by carneval in Rio de Janeiro. She would have all the fluffy clothes, big feather thingy on her head and big, wing like things on her hands. When she uses her Q or ultimate, a sparks and fireworks would pop. Also Evelynn's costume should be more provocative as the real counterparts are.
Instead of lamp post he would have a broom stick, working jeans and a baseball hat. His joke could be a refference to cleaning or education system. Also whenever he hits you with a broomstick a cloud of dust would appear as he is cleaning.
She would have white clothes, a white cap that chefs use. Her weapon would be a giant tomato surrounded by four kitchen knifes. He voice should be changed into french like because we all know that frenc people are famous chefs. When she dies, tomato would splat and knifes would go in air and then land beside her, stabing in the ground.
His carrapace would have yellowish tone, when he walks around you should hear a slight bzzzzzzzzz.
His beard would be all stained, one of his shoes would be split open, torn pants, dirty shirt and instead of 2 axes he would wear two pieces of wood and through both of them a big nail. Instead of his horned helmet he would wear a simple cap.
Whenever she htis with her hammer you would hear a squeaky noise, on her shiled you can see a big smiley face, armor would be all pink and look amost plastic like. When you use paragon of demacia Poppy would say Vrooom, vrooom in child like voice.
Instead of purple balls, there should be numbered balls floating around, her voice should also be altered. Her clothing could be provocative and tight just as the hosteses of those kind of shows. When landing ultimate she would say: AAAAAND THE WINNER IS!!!!
His staff would be a big pitchfork, when casting his stun instead of energy barrier there should be a wooden fence similar to those cow holding fences. His Q would be a cabbage, his W could be a huge pumpkin falling down from sky and his ultimate would be a giant tomato that splats when hits his target.
and the last one
Traveling Salesman Renekton
He would be lugging a huge suitcase instead of his blade, would be in an old checkerboard suit with a small hat and black shoes. His quotes should be the same as those on TV shopping channels. Like: If you buy this now you get the bonus, or WAIT, WAIT, WAIT, there is a special offer.
Hope you like these.