Clarke's comments come in the aftermath of defender Liam Ridgewell coming in for criticism after being pictured pretending to wipe his bottom with £20 notes.
Albion have dealt with that matter internally and Clarke claims the matter "is now closed".
But the Baggies boss has trust in his players to behave in the correct manner when they hold their festive celebrations this weekend.
Clarke said: "If the players want to organise a night out, then I've got no issues with that.
"You expect the boys to go out and have a good night together, spend a bit of time in each other's company, have a laugh and a joke and behave themselves.
"They are grown men, they are not children."
Supporters have been critical of the picture of left-back Ridgewell, which appeared in a Sunday paper.
It is not sure what action has been taken and Clarke would only say: "The matter has been dealt with internally.
"As far as we are concerned, it is closed and we moved on. Has Ridgewell been sanctioned? The matter has been dealt with internally. I don't want to talk about it."
The Baggies visit Arsenal on Saturday with Gunners manager Arsene Wenger coming under fire from his own fans after winning just three of their last 13 games.
Clarke believes the Arsenal boss is the victim of the lack of patience now evident in the game.
He said: "It's the new age in football. Wenger has done a great job for Arsenal. They've just qualified for the Champions League again.
"They've got a squad there that will surely qualify for Champions League qualification again this year in the Premier League.
"Just the way the game is at the moment, there seems to be a little bit of short term-ism.
"I know Arsene has been there a long time but people are starting to look at him and criticise him.
"The Arsenal fans can do what they want because it's not for me to comment on what they want to do and it's not for me to comment on how Arsenal run their business."
Clarke has virtually a full squad to choose from as Albion look to bounce back from successive defeats against Swansea and Stoke.
Goalkeeper Ben Foster is the only absentee as he continues his recovery from a second groin operation.