The thing about professionalism is that, the more professional a wrestler is, the more boring there. They are practically synonyms.
You turn up on time. You represent your promotion as an ambassador and rarely if ever have a bad word to say about it. You defend questionable decisions, you put over that which is dreadful or make light of the fans for caring too much because they don't understand the inner workings of the business. You'll do jobs. You might even say in the media that they believe yourself to be capable of leading the company, but you won't refuse to take a pin to the actual wrestler who leads the company.
You won't even entertain the option of jumping to the competition, publicly or privately, even if it would help your negotiating position. At the mere mention of the competition, you almost smirk. You are devoted to the real game in town. You feel it is your duty to work for and represent the company. As part of this duty, you scream your support of it on television constantly.
You are James Milner, or Seth Rollins.
On the other side of that particular extreme...
In an incredibly warped way, JBL was very likely seen as a professional within the über-screwed culture of WWE.
In any other sane environment, he was as unprofessional as it gets.
He partook in and drove a toxic culture that appeared to be encouraged to weed out the weak. If someone arrived and was seen to be taking the piss or otherwise not respecting the business, he'd cave their head in. The Public Enemy apparently didn't want to go through a table, since that was their thing to do, so Bradshaw and Faarooq put them through a table. And, before that, beat them as mercilessly as they possibly could using stiff shots that only very vaguely resembled pro wrestling strikes and throws.
JBL rendered the Blue Meanie's face a disgusting bloody mess at ECW One Night Stand 2005. Meanie reckons JBL assaulted him because Meanie had buried him as an "a**hole" after his brief 2000 run; JBL contends that the Meanie struck him first.
JBL took liberties with opponents in the ring, "hazed" or bullied or outright abused greenhorns, and even intimidated staff - Joey Styles, Justin Roberts - who weren't "the boys" and could not be expected to operate within that demented "culture".
A nasty person who delighted in making others miserable.