A couple of days ago, was sitting with my hearse in passive by LSC. with an ignition bomb. Low level comes up with a Simeon car, goes in, then starts driving away and I salute him. Just as he's about to drive off, I hear him stop around the corner and back up a little bit. He gets out, runs over to the Hearse, bam. Took me a second, realized Simeon car still sitting there - yoink - drove off. Felt bad so gave him half of what I made.
As for mugging idle players I do it all the time. Sometimes I'll sit in my apartment looking for players AFK sitting in their car. I always get a chuckle first watching the mugger drive off and then second when they eventually wake up and wonder WTF happened to their car. The best is when you happen across an AFK player and mug them - and now you can mug them for more $.
Another favorite troll lately is sitting in my apartment at RM (4, the lowest one - you can see the street level QUITE clearly, you look out at the RM garage and across the street to the WP garage area.) and leaving a Buzzard with a sticky or three underneath it (if you throw them into the back seat area, they go through into the underside) then waiting until a player happens by and looks overjoyed to see a convenient Buzzard. They take off all excited and get right past the window and BAM.
Since they changed where you spawn when you drive out of RM, it's become a lot more appealing. Plus, the low level apartment is great for trolling in various forms.