I used to have a British passport, Belgian identity card and an Italian diplomatic lasciapassare (literally 'let through'); the first because of my I wanted to avoid doing military service in Italy and Belgium - the latter two because of my Dad's nationality and employment status in Italy.
For fun I used to hand all them over to the Italian border police whenever I was going home - just to see the perplexed reaction. That was before the days of terrorism and marigold gloves for custom officers
Just thought I'd mention it in passing...but it's an interesting story that told above - I guess that's how some people end up living in airports....