When you see a classmate in class or at a study session, he is always very friendly towards you. however, when you run into him at an upscale party, he acts as if he does not know you. since you know he is a friendly person, what are you most likely to attribute his behavior to?

I believe the answer is: Situational attribution

Situational attribution refers to the process of analyzing other people's action depending on the situation that they're in.
for example, when you see a person steal a loaf of bread, you would automatically see that person in a negative light.
But if somehow you know that the reason why he steal the bread is to feed his children that haven't eaten in days, you would most likely start to lose your stance regarding that person.