If you're vegetarian, it's so simple. You just cut meat out of your diet. The issue is entirely in your own hands. Everybody else may eat meat if they wish, but as long as you avoid it yourself, you're a vegetarian. It's not so easy, however, to be a do-it-yourself republican.
For passionate opponents of constitutional monarchy, there are few options. Civil unrest and bloody revolution aren't acceptably democratic because, astonishing though it may seem, large numbers of people actually support the status quo. DIY republicanism appears to be the only choice. With a few practical tips, you could try it yourself.
The question facing tyro republicans is this: how do I cut the Queen from my diet? Or rather, how do I put an end to the thousand small daily gestures and habits that compromise my views?
Some things spring immediately to mind. First of these is the national anthem. True republicans will refuse to rise for Mrs Windsor, and certainly won't sing lyrics that hint at base subjugation. But even this protest demands a strong character, as it is certain to cause friction among the people standing and half-heartedly mumbling around you. Your protest will make them feel silly, and they won't like you for it.
Then there is the question of membership. Joining practically any British club or institution may be more than a true republican can manage. The vow of allegiance makes membership of parliament practically impossible. Crossing your fingers as you pronounce the vow is one thing - but how long will that get you through? What happens if you become prime minister?
The Church of England, too, is out of bounds, since everybody knows the identity of the supreme governor. And the armed forces all seem to feature royals among the colonels-in-chief and big-hatted admirals. Young republicans, similarly, will sniff at the prospect of joining the Scouts or Guides, as this also involves an oath of allegiance.
So much for the big decisions. We come now to more difficult problems - the daily transactions which cause agony to opponents of the hereditary principle. First among these is the routine in which complete strangers exchange tokens bearing the head of the monarch. I'm talking about cash.
Fortunately, technology provides a solution. With the advent of plastic debit and credit cards it has become possible for many people to do without cash altogether. If you should happen to be caught out occasionally, you can always revive the ancient system of barter. And looking ahead, EMU offers the prospect of an altogether new currency in which the paper money will be devoid of royalist idolatry.
A similar problem is posed by postage stamps. Some years ago, as postmaster general, Tony Benn attempted to introduce occasional stamps without the Queen's head on them, but without success. To this day, even special editions must all portray the monarch in silhouette. But clever republicans have stamps licked, as it were. They send messages by e-mail or fax - or, failing that, by hand or pigeon.
It is not just currency and postage that bear these built-in endorsements of the monarchy, however. Next time you go shopping, just take a look at the royal warrants on a box of Jacob's crackers or a bottle of Rose's lime cordial. To republicans, products such as these must remain out of bounds. The boycott starts here. For the same reason, you may decide no longer to shop at Harrods, or specialist retailers such as Rigby & Peller, which supplies corsetry by appointment to Her Maj. You think I'm going too far, perhaps. But would Scargill supporters buy biscuits bearing the warrant of Margaret Thatcher? Would left-wing Chileans patronise the shop that provided pants to Pinochet? I think not.
The biggest problem, though, is linguistic. For hard-line republicans, it can be difficult even to speak of certain British institutions - let alone visit or join them - because their names include the word "royal". I'm thinking of professional associations such as the Royal Institution of Chartered Surveyors. Charities ranging from the Royal Society for the Protection of Birds to the Royal Association In Aid of Deaf People; hospitals from the Royal Marsden to the Royal Free. Royal academies for arts, dancing, dramatic arts and music. There's even a royal borough, Kensington and Chelsea.
But what's in a name? You might think republicans could be less pernickety. They could overcome this minuscule problem by dropping the word royal. But that's not always possible and can lead to terrible confusion. I'm no race-goer, but I do know that Royal Ascot is not the same as Ascot. And the Bank of Scotland, crucially, is not the Royal Bank of Scotland.
Anyway, republicans aren't the only ones who set great store by names. Only last month a bunch of writers and actors created a stink when somebody suggested adding the name Jerwood to the Royal Court Theatre, by way of thanks to the donors of a large cash sum. Oh no, said these dissidents, you can't stick the name of some grubby commercial outfit on our beloved theatre.
Perhaps now you can understand how upset republicans felt when the National Theatre became the Royal National Theatre. Some haven't been back since. For republicans, there's no escape. You can't even go abroad, not unless you're willing to get a passport, an emphatic reminder if ever there was one that you are merely a subject of Her Britannic Majesty. It's either that or an illegal sea-crossing. But just think: if your boat capsized, would you be willing to be rescued by the Royal National Lifeboat Institution? Like I said, it's easier to give up meat.