Hoseok was great at reading people. Especially the members. Especially Namjoon - the guy kept so much inside, Hoseok could practically sense the pent up frustrations and repressed feelings radiating from his body heat. 

Kim Namjoon was a complicated person, hard to read for a lot of people except for when it came to one thing - because it certainly did not take a rocket scientist to figure out when Namjoon was mad.

Or: Hoseok figures Namjoon’s feelings out