Soft spot is when you like a boy/girl and you'll do basically anything for them. You could be mean to anyone but when it comes to them you're the nicest person on earth. You do the most just to make them happy etc
A soft spot is a topic you have used to invoke a dramatic and negative emotional reaction from the other person, said with a sing-songy high inflection.
"You know, I have the best abs ever!"
"Yeah, but your mom is dead."
red-faced and clench-fisted "I hate you."
"Soft spot"