So... I believe what you're looking at was caused by
LE ME.
This, ladies and gentlemen, is the result of stalling an Acura DN-X/Honda Dualnote. Only to be done with a clutch-supporting wheel, requires like 3 or 4 attempts before getting it done due to strange timing these cars require.
Why I did that was because I was a bit bored, and wanted to show people a strange bug, maybe something to laugh or at least smile at a bit.
Before you bash my skull in, I just want to say that I was NO IDEA it could affect other people in the lobby in a negative way. Please don't try to say that I was trying to troll/annoy anyone in the lobby, because I don't do that unless someone deserves it, and that lobby was filled with nothing but nice people.
My apologies!
EDIT:
From what I've found online and after asking some friends on GT5 I found that it actually is NOT the cause. A few of my mentioned friends had this problem as well. They are 100% sure they did not see a Dualnote/DN-X in their lobbies.
So I guess we're still not quite familiar with this case.