When I was in middle school I drank it black too look like a tough guy, and would elicit no reaction to basketballs landing on my head, same reason I don't even flinch when I'm drinking cheap harsh scotch now.
That being said, the bitterness of coffee black doesn't bother me much, I used to eat coffee beans when I was little and found myself in grocery stores. I guess it's more flavourful this way, it's nice for a change.