Dick Advocaat has warned his Sunderland players not to cross him if they want him to keep the smile on his face.
The 67-year-old Dutchman will send out his Black Cats team for the first time at West Ham on Saturday having spent the last four days trying to put his stamp on it following his appointment as Gus Poyet's replacement.
He has been happy with the response he has had on the training pitch so far and remains confident he can steer the club out of a second successive relegation battle.
However, he had a warning for his players as he prepared for the first fixture of a crucial nine-game mini-season.
Advocaat said: "I always say it is quite simple: if they do what I want on the pitch and in training, I am a really nice man; but if not, I'm not a nice man, and it's good when they know that.
"So far, I have been very friendly to them."
Advocaat was handed the reins on Tuesday following Poyet's departure the previous day, although he revealed he had first been sounded out about a possible vacancy by an agent up to four weeks previously.
But when the call finally came from Sunderland on Monday, he had few qualms about accepting their offer of employment.
He said: "In principle, every thing you do in football is a challenge and you want to do as well as possible. But we are now in a situation where we are playing more or less at the bottom of the league, so something has to change.
"In Holland, we can see all the games in England - everything is on television, so I knew the squad, I knew the players, plus the fact that we have a great stadium and great fans.
"With the support of them, we must do it. I have a good feeling about the squad after the last three days, so why not?"
The Black Cats head for Upton Park sitting just a point above the drop zone as a result of their 4-0 home defeat by Aston Villa - which proved fatal for Poyet - and Burnley's stunning 1-0 victory over title contenders Manchester City last weekend.
However, despite spending much of his managerial career fighting for trophies and working on the international stage, Advocaat is not fazed by the task ahead of him.
He said: "Everything you do is a challenge and this is a big challenge because this is a big club. We still have everything in our own hands, we are still one point ahead of the others.
"We have the same games to play, difficult games like the others, so we have to do it. Don't look too much to the other sides, just look at your own team, that's important."
Sunderland have won none of their last six league games and have scored only two goals in the process, and Advocaat will have to find a solution to the problem of how to make best use of January signing Jermain Defoe - something which eluded his predecessor as his tenure drew to a close - if that situation is to be addressed.
He said: "Defoe is, like all the others, a very important, key player in this squad, so we have to bring him into situations where he can play in front of the goal because that is his skill."
Winger Adam Johnson could be part of the answer following his return to training after a club suspension, imposed following his arrest on suspicion of sexual activity with a girl under 16, was lifted, although Advocaat was giving nothing away on that front.
He said: "The club has made a statement about it and there's no reason for me to add something to that. He has been training from Wednesday, and we will see after training who is available and who is not.
"In principle, he is available for selection."