I think this happens pretty regularly in the modern world.
One thing worth mentioning...blackout drinking. People might do this when they are in blackout...inhibitions are lowered and the person is unable to form a memory of what happened. Just have hazy recollection, maybe some evidence and a whole heap of shame the next day.
The temptation is to push it away, pretend it didn't happen or pretend noone noticed.
If it is disturbing the people he is messaging maybe someone can point this out and suggest the link to being drunk. That might not be taken very well?
P