Working class people aren't less intelligent than middle class people. The classes in Britain are not genetically distinct populations with different innate qualities. Middle class people do stupid things too. (That's leaving aside whether eating a hot breakfast is stupid at all).
People who haven't got the money for higher education make choices in the same muddy land between rational and irrational that we do. George Orwell put it best (of course):
Road to Wigan Pier Chapter 6
When you are underfed, harassed, bored, and miserable, you don’t want to eat dull wholesome food. You want something a little bit ‘tasty’. There is always some cheaply pleasant thing to tempt you. Let’s have three pennorth of chips! Run out and buy us a twopenny ice-cream! Put the kettle on and we’ll all have a nice cup of tea! ... Unemployment is an endless misery that has got to be constantly palliated, and especially with tea, the Englishman’s opium.
Incidentally my breakfast this morning was an avocado. And I haven't actually got round to eating it yet. Yes, I am a middle class twerp :-)