Last time I crossed the jumper cables on a car, it opened an alternate dimension, where I found myself on a planet surrounded by women that looked like Petra Nikova and I quickly discovered that I was the only man. Needless to say, my fuses fried and it ended the "reality" before it really began. If you want my opinion, I'd try to cross juper cables every chance I got.
Just joking. I used to wok as a mechanic and I've seen all sorts of jumper cabled crossed. Seriously, check your fuses, that's what they're there for. If nothing is wrong there... no worries.