i mean, the supernatural set was always known to be awful to work at, from people who worked behind the camera(for like an episode or 2, not regular) sometimes going on places like reddit(places like r/askreddit and or r/television) and talk about how awful it was because the main actors would purposefully mess up scenes just to mess with the crew.
and yeah, he better be nice to fans, they're his bread and butter. they literally pay to meet him, since it's always at convention meet and greets. but he's also known for making fun of fans, especially shippers, but jensen does it too.
he's an ass regardless if he's nice to fans imo. constantly getting into drunken fights and being an ass on twitter(not just the psh situation, he'd always go on rants talking shit about people. or like the time where he was throwing a fit because jensen didn't tell him about the supernatural prequel that was still underworks, and likely wasn't allowed to talk about it), that to me is enough to call someone an asshole