No line to the women's toilets will ever come between you!
This one sounds painfully obvious when explained, but we'll be damned if we can't think of a couple who doesn't make this mistake.
Studies show that it is actually better to keep your fun time separate, especially when it involves a hobby that one partner likes and the other just tolerates. A 10 year study showed that short of murder, the absolute worst thing a couple can do is engage in activities that only one partner enjoyed.
Like sleeping with other people.
All other things being equal, those couples reported the least satisfaction with their marriages. And the couples with the cojones to admit they have more fun keeping hobby time separate report greater happiness with their marriages than the fools who forced each other to co-enjoy their crap hobbies.