During the finale, Sam is having a hard time with something. Maybe the pressure of beating the Leviathans is getting to him. Maybe he's worried about Dean. Maybe he's just having a bad morning. He blows up at Cas. Cas, in his infinite and now slightly-off wisdom, deduces that Sam requires some comfort. What he does is up to you, but Sam is both bemused and deeply touched. Can be gen or Sam/Cas - just nothing explicit.