I had a friend in college who, for a while, bruised very easily, so much so that one of our mutual guy friends quietly and gently asked if everything was okay between herself and her boyfriend. The girl laughed (genuinely) and said they were fine, she was just a klutz!
Turns out it was a malfunctioning spleen that caused her to bruise so easily, so she had it removed and the bruising stopped. The bruises did look pretty bad, though.