anal ants
The sudden, acute onset of an intense itching sensation of the anus in which immediate action must be taken in order to gain relief. The sensation is compared to the feeling of a mosquito biting the rectum, and/or ant bites when accompanied by stinging and burning sensations.
I was saying my wedding vows in front of 300 people when I was suddenly stricken with a horrible case of anal ants. There was nothing I could do but squeeze my butt cheeks together and pray it would go away.