We've all got a mate with a particularly scruffy car - a mountain of old McDonald's cartons and Lucozade bottles splayed across the back seat, smelly gym kit stuffed into the footwell and, frankly, God knows what in the boot.
But it turns out you could actually get slapped with a nasty fine for such rank housekeeping in your car - though the DVLA aren't going to start rummaging around the back seat of your Nissan Micra, thankfully.
Nope, instead it relates to the condition of your number plate, with potentially hefty penalties for motorists who drive around with a grubby one.
Drivers who have license plates that are dirty or obstructed could face a fine of up to £1,000 ($1,400), as it's a violation of the legal requirements - which state that license plates should be made from a reflective material, the front one should display black characters on a white background while the rear one should display black characters on a yellow background and that they should not have a background pattern on them.
For motorbikes, things are slightly different, with number plates displayed only at the rear of the vehicle. Two-line number plates are standard for motorbikes registered after 1 September 2001, and it is against the law to display a one-line plate - regardless of the date of registration.
There are heaps more driving laws that most people probably aren't aware of, too.
We're hoping you knew that it's illegal to use your mobile phone while driving or while you're in the car with the engine on, though one you may not have heard before is that if you touch your phone while using the Sat-Nav you could be fined, The Sun reports.
You can also be fined if you throw rubbish out of the window, and it's illegal both to smoke in the car with someone aged under 18 or to leave a parked car with the engine running.
Obviously, most of them sound like quite a blatantly bad idea, but we're guessing most of you had absolutely no idea that they were actually against the law.
Plus, did you hear the recent news that new drivers may be banned from driving at night? The plan would be introduced as a means of helping cut the disproportionately high number of deaths among drivers on UK roads, and might see new road users banned from driving after dark for up to two years. Another one to keep an ear out for!