verb. To agree to attend an event or gathering, but cancel at the last minute due to external circumstances, especially if one has made a habit of such behavior.
noun. The act of monganing.
Billy said he was coming to the party, but we didn't expect him to actually show up. Sure enough, his house flooded and he monganed, just like last week's happy hour, when he was in that car accident.
Tina was supposed to go to the game night, but she had to work late again, so she pulled a mongan.