Funny people saying this is a case of bin men being victimised or treated badly. If a senior council worker turned up at your house and did the same thing they could expect the same consequences. It's not a question of criminal damage or whatever people want to argue about a snowman being a temporary thing, it's a case of conduct and this guy acted like a tool and won't even apologise.
Further, he's an agency worker and not an employee. So he hasn't even been 'fired', he's been told his services won't be required any more. You can say that's harsh as well, but the fact is that if you know you don't have employee's rights, you should probably be even more careful about not behaving like a moron.
All that being said, if it was my decision the guy would just have a stern warning rather than actually being let go.