But its annual leave that he's fully entitled to. Whether he uses it to jet off around the world, or sit at home in his boxers chilling out in front of the TV, that's of no business to his employer and unless he works in a particular industry or position where he may be required to be contactable out of hours (and he would usually be remunerated accordingly), they should leave him alone.
I respect your position but work to rule and don't moan when you're managed to rule. That or get a better job/manager

..Doing stupid things like staying up all night so ending up sleeping through the next day till early evening.

