Unreasonable Behavior
When a judge grants a divorce without requiring one side to prove that the other has done them wrong, the divorce is known as a no-fault divorce. Basically, all you want is a divorce, and that's acceptable. These weren't done in England for a long time. Instead, parties had to show that their spouse had engaged in "unreasonable behavior," which is what prompted them to file for divorce in the first place. There are hundreds of diverse behaviors that fall under this broad category, some of which are significantly more irrational than others.
There have been cases presented to the court when the most absurd justifications for divorce were given. One man claimed that despite his wife cooking tuna casserole for him on a regular basis and with malice, he detested it. A woman alleged that her husband made her dress in Klingon garb. Other justifications have included tossing out stale cold cuts, fiddling with the TV antenna, and allowing a pet tarantula to sleep close to the bed.