How to remove rubber/glue residue?
 

So my lip spoiler became loose and I decided to just tear it off. Part of the spoiler was attached using double sided 3M tape but most of it was this stuff. It feels like hard rubber and is stuck onto my trunk.

Anybody know what it is and how I can get it off?

That looks like melted 3m double side tape to me? If it is, get some soapy spray and a fishing wire and slowly "cut" underneath it. There will still be some light residue left and just use a polish or use a rag and rub it off
Edit: upon further inspection, I think it is likely either a silicone adhesive or an epoxy...silicone should be able to be removed via the above process, but I'm not sure about epoxy

that's the black urethane... usually used for stationary glass installs.

here's what you need to do:
heat up each blob of urethane with heat gun.
cut off excess urethane with razor blade or wire as close to the paint as possible
(you can also sand it with sandpaper when its cold, just make sure to tape surrounding areas with duct tape)

once it gets to a thin layer, heat it up again, soak it with paint thinner this time
let it soak as it will weaken the urethane, this will take a while
then just scrape off the excess layer of urethane with a plastic razor edge

polish the area when everything's done

its easier said than done, the key is to work it slow careful not to cause more damages