Now that's someone who isn't mature for his age!
Angry Kramnik

fabelhaft, I enjoy all of your postings about top level chess. The video I got from your link had Kramnik's reaction at 7:05. I guess Kramnik is not impressed with young Napalm-nasty.
If you think Kramnik is a bad loser, I would argue it is because he's had so little practice at it.
He used to be very difficult to beat but has gotten more practice at losing games the last years. 2010-13 he has lost 30 games of classical chess, 2000-03 it was in all 6 losses. Kramnik really changed style a lot the last years, from very safe play with many short draws to a much more exciting and risk taking style.
Some fifteen-twenty seconds after 16:05 on the video below Kramnik doesn't look happy after losing to Nepomniachtchi. His gestures towards the winner could be a quite understandable reaction or being a bad loser depending on how you see it. Still, interesting to look at the video :-)
http://chesstv.com/en/broadcasts/225