I know Sens fans hate him, but I'm not sure why. Can someone shed some light on this?

Plz? Anyone?

The main reasons Sens fans don't like Yashin is because he held out of his contract for more money. He did this a couple of times and sat out an entire season in 1999-2000. Earlier in his career he sat out until January I think when the Sens eventually gave him a new contract. In 2000 they let him sit the whole year and he was still forced to play the final year of his deal.
THe fact that Yashins last 2 playoff years in Ottawa he had 1 point in 2 playoff series did not sit well in Ottawa. There were other things as well like the fact that he promised to donate $1 million over 5 years to the National Arts Centre in Ottawa and after a year or 2 of the donations he backed out over a disagreement about his parents getting money from the Arts Centre.
He did a lot to piss off the fans of the Senators, but was traded for Spezza and Chara so some good did come from him.