Twitter erupted when the Republican National Committee chairman implied that Democratic nominee Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE should smile more after her appearance on NBC News for a presidential forum on Wednesday night.

"Hillary Clinton was angry [and] defensive the entire time — no smile and uncomfortable — upset that she was caught wrongly sending our secrets," Reince Priebus tweeted after the event.

@HillaryClinton was angry + defensive the entire time - no smile and uncomfortable - upset that she was caught wrongly sending our secrets. — Reince Priebus (@Reince) September 8, 2016

Clinton's campaign fired back:

Actually, that’s just what taking the office of President seriously looks like. https://t.co/Pyn92mesom — Hillary Clinton (@HillaryClinton) September 8, 2016

Twitter users took notice of the comment on the former secretary of State's expression while answering serious questions.

Did you just...tell the former Secretary of State to smile? https://t.co/UtIYTLfInX — Rob Flaherty (@Rob_Flaherty) September 8, 2016

Stop telling women to smile. https://t.co/PxavqLvv7a — Elizabeth Plank (@feministabulous) September 8, 2016

Trump attacked US generals and praised Putin and thats ok but Hillary didn’t smile enough. Got it. https://t.co/xnA2mt2OrD — Josh Schwerin (@JoshSchwerin) September 8, 2016

National moratorium on telling female politicians to smile more, okay? thx https://t.co/cGjRDN01yw — daveweigel (@daveweigel) September 8, 2016

Also, did Trump smile? Is a smile an appropriate response to Qs about the VA and war? Chrissake. — daveweigel (@daveweigel) September 8, 2016

When the best you've got on your opponent is "smile more," that's how you know you've lost tonight's forum. https://t.co/NTEEVErNk7 — Teddy Goff (@teddygoff) September 8, 2016

MSNBC host Joe Scarborough got into hot water earlier this year when he told Clinton to smile after she won several big primaries, which many saw as a sexist comment.