Here, let me give you a few examples
for starters they fight about all kinds stupid sh*t all the time, (friends, family, work, sex) I mean I highly suggest you go back and rewatch season 5,6,7,8,9,10
2) Leonard gave her a engagement ring that was made out of diamond drill bits, who does that?
3) Penny took off her engagement ring at work to flirt with other men. First off if Penny feels the need to do that, they should not be getting married
4) i highly suggest you go back and rewatch season 5,6,7,8,9,10 they had some pretty stupid fights over nothing
5) their tradition of stupid fights with Lenny will probably go on for the rest of tbbt because it has always been there and it’s part of the shows history