The psychological sickness one contracts when Mumfords and Sons backs out as the headliner of the music festival you're attending. Symptoms include, but are not limited to: intermittent frowning, being teased by your peers and randomly storming off in the middle of the show that replaced Mumford and Sons.
"Janet was really looking forward to seeing Mumford and Sons play at Bonnaroo this year. When they were suddenly replaced with Jack Johnson, she came down with a bad case of The Mums."
by Chicketychina11 June 21, 2013