Oh man is he annoying. The best thing to do is to start longsword 3 pots and all in level 1 with a full Broken Wings auto combo as he will only have his Cull the Meek, if he doesn't die but is relatively low you can bully him till he next recalls. However, if he starts Ruthless Predator play safe and farm as best as you can backing off when his fury bar is full and start harassing him when you reach 5. You can slowly lower his HP bar in order to cheese him at level 6 with a quick all in. If you see a Renekton picked, DONT pick Riven unless you are smurfing or really confident in the matchup. In this lane warding is essential in order to survive the inevitable ganks as Renekton will snowball off a kill and can easily coordinate ganks with his jungler due to his empowered Ruthless Predator stun.