When in a mosh pit of such viciousness that you are pushed and pulled in all directions and manners. Your personal space/ability to stand freely is violated to such a degree that you have no choice but to leave the mosh pit or suffer the consequences - e.g. lose a shoe/eye or get trampled on.
This usually occurs when surrounded by those who have no mosh pit etiquette or are in a mosh pit for the first time coupled with their first drinking experience.
The feeling of violation stays with you long after the experience.
Person 1: How was The Fray concert?
Person 2: Terrible! I was moshraped by a bunch of tweens during the support act!