Inflected form of
TOS when applying it to another person where the subject will either
flag or manipulate the victim's account (through trolling, or some other means) as-if the victim had violated the terms of service for a particular site, thus getting the victim's account flagged and/or banned.
This term originated back in the days of the early
internet when the majority of the
USA would use America Online as their service provider. During those times, TOSing was considered a legitimate form of "punting" a user.