GameStop CEO Ryan Cohen wants to buy eBay, but the e-commerce platform isn't keen. GameStop; Smith Collection/Gado/Getty Images eBay has rejected Ryan Cohen's $55.5 billion takeover offer. The GameStop CEO made an unsolicited offer earlier this month. eBay's chairman said the offer is "neither credible nor attractive." eBay has turned down Ryan Cohen's unsolicited offer to take over its business. The online marketplace giant said Tuesday that it has officially rejected the GameStop CEO's $55.5 billion bid for the company. "We have concluded that your proposal is neither credible nor attractive," eBay's chairman wrote in a letter to Cohen.…