And now there's another reason to hate Mondays as a study reveals that not only do we feel ugliest on the first day of the working week - but that information is used by cynical beauty companies who cash in on our insecurities.
The study, by London-based global media agency PDA, was designed to discover when women felt at their most unattractive - and therefore at their most vulnerable to be marketed to by beauty firms.
The company questioned women aged 18 and over to identify when they feel most vulnerable about their appearance in order to determine the best timing for beauty product messages and promotions.
The results showed that 46 per cent reported feeling at their worst on Mondays.
Reasons cited took in stress, lack of motivation to make an effort and visible and emotional effects of the weekend showing on the face.
The report showed that women feel their best on Thursdays, when the working week is coming to an end and the weekend is in sight.
The information gleaned works both ways. While sometimes it suits a company to catch a customer when they're feeling low, in other situations it might be best to engage with a customer feeling happy and confident.
'Identifying the right time to engage with consumers with the right message is Marketing 101,' said a spokesman for PHD.'But when you are trying to connect with women on so personal an issue as appearance, it can be even more important to understand the wrong time as well.'
Monday becomes the day to encourage the beauty product consumer to get going and feel beautiful again, so marketing messages should focus on feeling smart, instant beauty and fashion fixes, and getting things planned and done.
PDA say: 'When it comes to engaging with women at any level, knowing where she is on her personal attractiveness index, and the appropriate messages relative to that information, can only make for a more productive exchange.'
For the consumer though, it undoubtedly means one thing: Less money in the bank.