There are big fat sludgy ones, shiny little round ones, and frankly I'm pathologically averse to all of them purely on the basis my parents tried to force them on me as a youngster.
One of their principle purposes seems to be being so unattractive that in rejecting or laughing at them we meet them halfway and half-follow the rules - or eat other vegetables, the metaphor is slipping now - without really noticing.
That's why people enjoy decrying health and safety urban myths about the wrong-shaped bananas and conker matches being banned even though they're not quite true. And perhaps they serve us well for all that, even if it's only in making us more careful when smashing each other's nuts.
Which is how something first mentioned as a joke on television 11 months ago has bloomed into an embellished remark on radio and then SHOCKING CLAIMS in today's newspapers about the terrible new health and safety-based world order.
Back in January during an on-air experiment listening to a distant planet to see if it was emitting a radio signal which might indicate intelligent life, Professor Brian Cox and Dara O'Briain joked they'd had to comply with BBC guidelines to do it.
Despite the fact the listening, while very technical, is in alien-discovery terms akin to a paper cup and a piece of string which doesn't even have a cup on the other end, and it was about as likely to discover extra-terrestrials as it was Sienna Miller's bra, there was some light-hearted concern about what might happen if there was a close encounter.
Fast-forward 11 months, and Prof Cox joked: "We decided to listen. You never know. The BBC actually said 'You can't do that. We need to go through the regulations and health and safety and everything'... It was incredible."
Maybe the BBC did say that - it certainly has the ability to flap about the silliest of things while ignoring decades of really serious stuff, like child abuse - but what's more interesting is that such rules do exist.
Not at the BBC, which manages to make a charter pledging to inform and entertain the nation last for 37 pages of barely-translatable tripe, but at the International Academy of Astronautics, a body we really ought to pay more attention to.
It is the IAA which set up SETI - the Search for Extra-Terrestrial Intelligence - and their panel of experts which search the known universe for signs of bacteria or lizard people and every kind of life form in between.
And SETI have rules for what to do when the little green men give us a wave, or a laser beam, or a brief burst of rock'n'roll on the airwaves.
The rules are, as rules are wont to be, detailed, well-intentioned, and ridiculous. But they're worth noting, just in case E.T. lands in your garden and it's you who will make first contact.
Firstly you have to verify beyond all reasonable doubt the contact is genuine. Seeing as this may need an autopsy to prove it's not a child in a Hallowe'en costume, first contact has now turned into first intergalactic incident and star destroyers are on their way.
Then you have to tell the relevant national authorities and observers, then the international scientific community, and when it's all been verified by the nerds and the airwaves have been locked down and everyone's had a jolly good think then, and only then, can you respond to the contact.
By which point, of course, E.T. will have got bored and zoomed off, died of methane deprivation, or killed us all with ray-guns or a terrible new disease.
The rules are based on the hope that it will be a well-behaved member of the scientific community who gets the radio message first, when anyone who knows anything about humanity, coincidence and the way dramatic-discovery stories work knows it will either be a maverick Doc Brown character or a quiet, utterly bonkers enthusiast in his garden shed.
The real rules for the discovery of extra-terrestrial life will therefore be more like this:
* Receive 'hello'And after that you could watch E.T. fade away into the galactic distance, thinking there was no-one here to talk to, and realise that while Earth might be missing out the spaceman probably had a lucky escape.
* Scream again
* If English, make a cup of tea
* Send a tweet
* Ring Max Clifford
* Be arrested for inciting a riot
* Fend off the Daily Wail
* Fend off Professor Brian Cox
* Fend off Sienna Miller's breasts
* Barricade self in shed
* Be praised as a scientific genius
* Be accused of bringing apocalyptic plague
* Get tired of the whole thing and say you made it up
It's all very well having rules for how we handle the inevitable day when we discover either sentient life or interesting bacteria, either of which could easily wipe out humanity if we weren't careful, but if no-one knows about the SETI protocol it's all rather a waste.
On top of that it will be a farce if the rules aren't even capable of being followed; most of us would have no idea how to ring the geeks and tell them there's a space shuttle on the lawn, so we'd call the police instead and they generally take a dim view of intruders.
But then some rules show only how fit they are to be broken, particularly if they remove from humans' first contact with aliens the normal, human behaviour which at its best is about all we've got going for us.
If they come here, it's to see what we're like and the one thing the rules should state is that we show them some humanity, not rules and guidelines. Especially if we want our own health and safety to last past the point they get fed up with regulations and unholster the death ray.
So should you receive the radio signal or find a lizard-man in the flower-bed I'd advise ignoring everything SETI says, smile, and say hello. First impressions are important, and so is politeness.
Then ask him if we can have Elvis back.