He does not have to say 1 word about being fired and what he said. He just needs to say that he is now pursuing a different avenue. His former boss can not tell any future employer that he was fired and the reasoning behind it. BTDT from experience.
I'm an IT manager with one of the largest contracting companies in the US. I do a lot of hiring (and some firing), and we get many college grads who are looking for a toehold in the IT industry. Heck...I've BTDT too! Many people have been fired from positions - rightly or wrongly - over stupid stuff. Rest assured, if you can put 5 years from that firing, it may not even be a factor. Until those 5 years pass, however, it can be a fun little dance.
I will echo the quoted post above. If a 20-something with no other job experience gave me a big ol' story about how he got fired because of an "aggressive customer" or that it was a "learning experience", my company wouldn't even give him a callback. Unfortunately, companies care more about a person's ability to make them money than to be a mentoring opportunity for a young person. Hiring managers know that few people have stellar histories, and many jobs end due to personality conflicts and unfair circumstances. We don't always get along with our co-workers and supervisors. But I don't want to focus on that. I care about what the person can bring to our team and company. What are they looking to accomplish? What kind of person are they?
I would humbly suggest that this young man say something like, "It was a great learning experience, but there was no room for career or skills growth. I wanted to find a company that would provide me an environment where I could expand my skill sets in an industry more appropriate to my training." Done.
In my experience (and might be only my company), if we're called for a reference, we are allowed to say: 1. How long the individual worked there, 2. what their salary was and 3. whether they are eligible for rehire. And oftentimes, references don't even bother with #3.
Telling potential employers all of the less-than-flattering details of one's previous job can really backfire in this economy. However, studies are indicating that IT hiring is due to be up in the next 18 months, particularly in IT security, Incident Response, big data (which goes hand in hand with database management), mobile security/app programming and specialty programming such as Java. I wish him luck and success!