Everyone keeps saying wreck it or set it on fire or whatever, that still won't help him if he is 8K in negative equity it won't pay off his loan and he will be responsible for the 8K not covered. They wont want payments either they want it all NOW.
Sell the car you have the least or NO neg equity on then drive the other one while paying down the payment more so you get the neg equity GONE.
I'm also in agreement with the others who are telling you to get your priorities straight. Don't mod your car if you are so upside down on your car pay that shit down man your only making your life harder by not doing so.
Sounds like your money management skills and priorities SUCK! No offense.