Many have suspected it for years, but now research has proved that driving with your other half sends your stress levels soaring.
Motorists feel four times more anxious if their partner is alongside them in the car, according to a study.
Researchers at Allianz Insurance said: 'Drivers are happier, more confident and focused when driving by themselves.'
As well as quadrupling stress, 'partner pressure' was found to make motorists feel twice as rushed, increasing the risk of them having an accident.
Drivers told pollsters that the addition of any passenger increased their stress levels but that they were least relaxed with their husband, wife, boyfriend or girlfriend in the car.
The study revealed that women are more wound up by men than vice versa. When driving with their partners, only 32 per cent of women said they felt relaxed, compared to 43 per cent of men.
Children also featured in the top five stress factors. Only a quarter of women and a third of men felt calm with their own children as passengers.
Other car stress triggers were other people's children, parents and other family members.
Almost one in five motorists listed city centres as the most stressful driving locations. They were followed by town areas with 8 per cent, motorways with 8 per cent and dual carriageways chosen by 5 per cent. More than half of those polled cited country roads as the calmest place to drive.
But motorways divided the sexes, with almost half of men feeling relaxed when driving on them, compared to less than a third of women.
The research also looked at times of day that drivers feel most rushed - commuting to and from work, travelling to appointments such as visiting the doctor, and driving children to school.
The biggest worry for motorists was 'other drivers', followed by tailgating and those with aggressive road rage.
Jon Dye, CEO of Allianz Insurance said: 'The tales of back seat drivers and in-car arguments we're all so familiar with, cause stress and distraction when drivers should be feeling calm and focused.
'It's important that motorists and their partners are aware of the risks a stressful environment in a vehicle can create.'