@TTH,
I don't think it will effect him permanently - it will in the shorter-term. If he were to apply within the company in the next couple of years, I am sure that his comment will raise a red flag. Although it may help him if he comes forth and explains he was stupid and immature and has outgrown that.
On the other hand, he has been telling us this same story the past year - each time he does something stupid and immature.
It wouldn't affect him outside the company as this would not be given outside.
I agree venting is a good thing - but venting is what you do with your friends and family, not in something that is a permanent record.