What if a big black dude punched me in the face?
Depending on where on your face he punched you, you'd have a giant bruise, some cuts, a black eye, or all of the aforementioned.

What if a dead body fell on my car and I didn't have insurance?
You'd have to pay a lot of money to get your car fixed, unless of course the people who dropped the body approached you and offered to pay for the repairs.  Also, if the people who dropped the body DIDN'T approach you and the dead body's death wasn't accounted for, you'd also be arrested as a suspect for murder!

What if I went to put on my shoe and a giant wolf spider was in there?
I hope you'd be putting your shoe on whilst wearing socks (otherwise your feet probably smell like crap that's been in a bucket in the sun all day) in which case the spider would attempt to bite you briefly before dying.  Having been protected (probably!) from the bite by your sock, you would only notice the sickening crunching feeling as you destroyed its exoskeleton and obliterated its organs.  Probably juices would get on your toes and on the inside of your shoe.  If the spider did succeed in biting you, you'd probably say something loudly along the lines of, "Ow, what the fuck?!  Shit!!" before yanking your foot out of the shoe to see spider paste all over your foot.  However, unless you have a specific allergy, the bite would do nothing because they aren't poisonous.

What if my penis touches the toilet when I'm taking a dump and I catch an STD?
Your doctor would laugh his or her ass off at you.  So would anyone else you told.  Unless you actually know people who are capable of sympathy, in which case they would laugh while saying, "Oh, that really sucks!"  Hopefully it's a treatable one.

What if I choke to death from drinking a soda because my idiot friends put toothpicks in the straw?
You'd die, and it'd be really easy for them to construe that as suicide.

What if I was locked in a safe and had to go to the bathroom real bad?
You'd pee/crap yourself.  And probably cry.  Try to do it in a corner.  When and if you were eventually released, you'd probably get laughed at again.  They'd be like, "It's that dude who got an STD from the toilet.  Euugh, what stinks?  Dude, he freaking crapped himself!  Shit, man, you were only in here for ten minutes!"

What if while I was in stuck in traffic on the highway a nuclear bomb explodes in the horizon like in that one scene in Terminator 2: Judgement Day?
You'd die, probably.  Eventually.

What if I crash my car while browsing radio stations and it so happens to end up on CAT COUNTRY 96.1 on impact and everyone thinks I secretly listened to country music when I die?
They'd probably think you had other secrets, too, and the newspaper would mention that you had gay butt sex with horses while wearing nipple clamps and a strap-on dildo (all of which could not be located, but they're sure it existed.)

What if those off color crumbs in my cereal are actually dandruff chunks and/or dust particles?
Then... that's disgusting.

What if my TV explodes and glass shoots towards me?
You'll get cut, possibly killed if you're unlucky.  I used to have a similar fear when I was a small child.

What if white supremacists surround my car while I'm at a red light?
Well, you'd probably look around yourself in a sort of confused manner, and one of them would probably reach in your window and try to pull you out that way, because they're idiots.  Luckily, you're smart and buckled your seat belt, so you experience some discomfort and more confusion until an angry black man jumps out of his own car at the red light and starts beating the living shit (and the nonliving shit, but not the dead shit--respect the dead) out of the white supremacists.  Other black people would join in.  Then you would all get arrested.

What if my friend pops a pimple in my mouth while I'm sleeping?
You'll probably...  you get pimples in your mouth?  Did I read that wrong?  That's disgusting, dude.

What if I snap my neck or back while cracking it?
You'd die, or start seizing violently and have to be hospitalized.  Maybe you'd be paralyzed or braindead or something.  I really don't think that's likely to happen.  But all the other ones are.  Yep.