I'm a huge (and terrible) car singer. Any time a song I know comes on the radio, I'm probably singing along, even if I don't really know the words. If the occasion calls for it, I might even go into full-on performance mode (I slayed "My Heart Will Go On" this morning). It certainly keeps the drive more entertaining.
I do sometimes wonder what other drivers think of me. Do they notice me singing my heart out? Do they think I'm crazy? Why aren't they singing along to their radios, too? I've never actually caught anyone looking at me, so I'd rather just imagine I'm in my own little bubble of awesomeness. We'll see if that leads to any embarrassing situations in the future.
Well, I don't drive so I can sing as much as I please because I'm on the passenger seat and no one gives 2 ****s about the person in the passenger seat.
I sing in the car, but not my heart out. But that's because I don't want to, not being I'm embarrassed or anything.
Every now and then when a high energy/power song comes on I'll go for it a bit more, but I'm still not bellowing as loud as I can because I'm content with singing moderately loud.