Razzing is playfully roasting someone or teasing someone. It could often be a close friend or family member.
It could be over anything but it could be brought on by something that might be revealed by a person that is a surprise to others. Something that could seem out of character.
Like a
guy finds out his very
tough and rugged friend really likes love songs or romantic movies.
His friends might razz him over that a little
bit for
fun.