Its easy to not end up in bad sport lobbies, regardless of how many cars you blow up. Simply do positive activities after a session of mayhem. Play some contact missions, alone or with others. Do a heist. Commend yourself regularly. (You can!)
The fastest way into bad sport lobbies is not by blowing up personal vehicles, its by being "reported" after blowing up personal vehicles. If you repeatedly detonate the PV of someone else sooner or later they're going to report you and that's when it its going to stick to you. If several players simultaneously report you, (Each person can report someone twice at a single time) well you get the idea. Its not good.
I've seen several crews operating this way. They find a lone guy, this lone guy doesnt take their 5v1 BS and take em on, and is pretty good. He embarrasses them, over and over by holding his ground, so they retaliate the only way they can... by simultaneously reporting him all at once. We're talking 6-10 reports of griefing all within the matter of minutes and boom the guy disappears from the session. Did he just go to a new session, call it quits or was he relgated to the BS lobbies? I don't know. I can only vouch for what I hear on the mic and in parties.
Personally, what ever comes at me. I kill, I try for the driver but if I have to take the entire vehicle, so be it. I've done this for over 18 months and the number of PV's I've blown up is in the thousands. Never once have I landed in a BS lobby or had my title changed too "dodgy player", (When this happens you're very close to being in a BS lobby and you bettter just bug out and do COop for a few days).
I stay out of BS lobbies because I don't kill the same person over and over again, giving them a reason to report me. I don't antagonize bitter packs of dogs, who attack together because on their own they wouldn't survive. Most of you know these as "Crews" and at the end of the night, when I'm done I start doing solo contact missions, several in fact. To clear and invalidate all those cars I blew up and any reports filed. When I log on the next day, I almost always get 2k for being a good sport shortly after.
The key to the entire BS lobby thing, is don't be a total prick and don't continuously pick on someone clearing out matched. I know several people who will stop what they are doing, and report players on the opposite side of the map simply for spawn killing a noob over, and over. Because when a lvl 300 is washing the floor with a 20, the game isn't fun for anyone.