Chinese speakers might think they know the difference between 伯父さん and 叔父さん, both read ojisan.
In Chinese Mandarin, the character 叔 is used to refer to brothers of your father only. It’s not used for brothers of your mother nor sisters of either side.
However, this is not the case in Japanese. In Japanese, both sides use the characters 伯父さん and 叔父さん to refer to male siblings of both sides of the family, as well as 伯母さん and 叔母さん to refer to female siblings on both sides of the family.
So what are the differences?
伯父さん is used to refer to your parents’ elder brothers while 叔父さん for younger brothers. Likewise, 伯母さん is used for elder sisters while 叔母さん for younger sisters.
As for the random ojisan on the street, that’s written as 小路さん. Funny huh?