play it straight

verb3

1. •
   To behave in a manner that is straightforward, honest, or sincere.

   • He added, "I think the American people want a President who will play it straight in foreign policy, tell them the truth." — 1992
2. •
   To avoid criminal behavior.

   • "But the best thing about him is that he always played it straight with us—never double‐dealed, giving us two and keeping one for himself." — 1976
3. •
   To perform a role in a manner that is not comedic or exaggerated.

   • And how can you not admire a man who could star in a stinker like Battlestar Galactica—and play it straight? — 1998