Twill's mother, demonstrating HMM behavior

Holiday Mother Mood (HMM) is a state of mind which some real-life parents (particularly Route 50 members' mothers) enter during the holiday seasons, not unlike PMS. While in this state, the afflicted parent will be more prone to directing anger at their child, generally taking on the behavior of a [superpants]. Common symptoms include intensified screaming, severe and rapid mood swings, frequent lectures, and threats of internet bans.

Twill's and Frosti's mothers were (respectively) the first two diagnosed victims of Holiday Mother Mood; however, many other parents have been identified as being susceptible to HMM since. As the days draw close to the day of celebration (such as Christmas), the condition continues to worsen, particularly if that day involves visits to or from relatives.

It is theorized that Twill's mother suffers from HMM all year round.

Kat's mother experiences severe HMM around the holidays of Thanksgiving and Christmas, so much so that they did not have a family Thanksgiving for three years in a row.