T shirts can be used very easily against another person in grappling. They can provide an anchor point for an untrained person to stiff arm against someone trying to grapple, making unclothed grappling methods much harder to pull off and much lower %
If you grab the whole back and bunch it over the near side arm it provides a good grip which also immobilises that arm, excellent entry to a really hard forward throw with one arm out of the way, and hard to break your fall with a wrapped arm.
If you grab the back with one or both hands you can pull it over and down on the head, obstructing vision, impeding arms, and providing an excellent handle to snap down and grab the waistband, which can then be used for a KO backwards throw like osotogari, or a powerful forwards hip throw
Choking someone out is very friendly, legally speaking, in my experience. It doesn't look like you did anything much. Drunk friend sleeping it off- who cares? A person with grappling experience will not kill anyone doing this, unless they are old and infirm, in which case why are you choking them out?