Dennis says that Mac sucks on pens at their apartment so often that he has to hide them.
In season 10, he's diagnosed with borderline personality disorder.
Bill Ponderosa is a classic example, being a lazy, overweight.
While Charlie trains Mac, Frank, Dennis, Dee take their bar-banter to the Internet with their own podcast.
Dee's also quite concerned that it makes her look like a pedophile.
While Mac and Charlie's Christmas traumas are genuinely horrible, Dee and Dennis' problems are a little less intense, as they whine about Frank never giving them gifts and generally being an asshole dad.