Student or Learner
Which does this "straight" mean? "frank,candid" or "stern, strict"? The translation goes for the latter, but I think the former also works.
ex)Imagine you're set up on a blind date with a friend of a friend...You say, "What do you have planned for this weekend?" "Oh, probably what I do every weekend : stay home and read Hegel," your date responds with a straight face...
It means 'with no sign of being other than serious'.
"I do 75 one-handed press-ups every morning," said 5jj with a straight face. His guest looked suitably impressed, but 5jj's wife could not hide her expression of shock at this blatant lie.