The former have been poisonous and indefensible. The latter carry the potential to do him far more actual harm. Hostility and criticism comes with the territory for any chief executive of the Scottish Football Association and Regan's immersion in the Rangers story has exposed him to plenty.
A sizeable proportion of Rangers supporters regard him as pursuing an agenda against the club. Around the rest of the country he is blamed for doing too much to help them, specifically being co-architect of the failed attempt to parachute them into the first division rather than the third. When Scottish Football League chairmen kicked out that idea, it was a very public bloody nose for Regan, Scottish Premier League chief executive Neil Doncaster and the Scottish Football League's David Longmuir, who had all put their names to the proposal.
Of the three, only Regan has endured death threats and a visit from Strathclyde Police counter-terrorism officers. "When you start to get threat messages on things like Twitter and start to get emails and letters through the post that are uncomfortable, let's say, then you have to listen seriously to what the police are saying," he said. "We have had visits from the counter-terrorism unit, we make no secret of that. I've had personal discussions with the police from the perspective of my own safety.
"It's never easy when the police get involved and your work life and personal life start to become interconnected. I've had the same conversations with police about people outside, police cars driving past outside my flat and so on."
He lives alone and, every few days, returns to England to spend time with his family. "At times that does make you wonder whether it is going to impact on your family and personal life. But it's never once made me think about walking away from the job. I don't see why a small number, a minority of individuals, should get in the way of us delivering what is right. As far as I'm concerned, I'm here to drive the game forward. Petty comments and small-minded behaviour doesn't interest me."
He had been an enthusiastic Twitter user but the volume of obscene messages directed at him led to him deleting his account.
Extremists making threats may not be allowed to impinge on Regan but others have it in for him, too, and their hostility may be far more significant. Many chairmen – and fans – took offence at his claim that Scottish football would suffer a slow, lingering death without Rangers. There could even be "social unrest" if they began life in the third division, he said. It sounded alarmist and sensational. Supporters mobilised and chairmen railed against what they regarded as scaremongering and bullying in order to give Rangers a soft landing in the SFL.
Dunfermline Athletic, Livingston, Clyde, Raith Rovers and Cowdenbeath were among the clubs to loudly speak out against him. There were calls for him to resign and some members of the SFL wanted a vote of no confidence in him, a matter which may yet be revisited. The SFA stood by him and he will not resign, yet the episode has been deeply bruising.
"What our plan was designed to do was to show the potential consequences for Rangers being below the top two divisions," he said. "I tried to paint a picture of the financial consequences if Rangers weren't at the top of our game and the challenges that would result for the clubs in the top division. The clubs have voted and we've gone through that process of them deciding what's right for the game. We've got to respect that and move on.
"I think we tried to be marriage-brokers. Let's not forget we sat down with the SPL and the SFL and their key directors were part of that team. Club chairmen came under pressure from their fans, there was a desire to sell season tickets and there was a concern that Rangers had to be dealt with in a way that recognised the seriousness of some of the challenges which had gone before."
There was further heat on Regan when an email he wrote to the other governing bodies was leaked. A reference he had made to Charles Green being briefed "confidentially" looked awful. "I have been personally vilified for trying to be a marriage-broker or a peace-keeper," he said. "There was nothing in that email which was secret in any way. The fact that it became a leaked email was quite surprising, because there was nothing in there that each of the governing bodies didn't know about. Rangers were aware of the discussion. Charles Green and Ally McCoist actually sat in the boardroom and agreed the plan for Rangers to be part of the first division. It was presented as being in the best interests of the game, from both a financial and a sporting sanctions perspective. All we ever tried to do was act in the best interests of the game, but the other clubs decided otherwise."
But what now? If league reconstruction was suddenly top of the agenda when it would have meant Rangers dropping only one division rather than three, then surely the issues still demanded to be addressed? "As far as the SFA is concerned, league reconstruction remains the single biggest priority. The component parts of reconstruction are still on the table. It's my job to try and bring people back to the table, restore unity and rebuild relationships so we can take the game forward.
"I can sleep at night knowing all I've ever done has been for the good of the game of football in Scotland. I am confident in my own ability and the board are confident in my ability. There's always going to be a small minority trying to knock you down. I am not here to win popularity contests. Football isn't about popularity. I'll continue to do what I need to do. If I upset people along the way, I know that's part-and-parcel of the territory with the job that I'm doing."
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