The U.S. Department of Defence put out a rather on-the-nose tweet about recognizing the signs of mental illness on social media Monday, triggering a wave of snide remarks that the message was aimed at U.S. President Donald Trump.

"Social media postings sometimes provide an important window into a person's mental health," the DoD tweeted. "Know what to look for."

The link leads to a page offering advice on using social media to help loved ones dealing with mental illness.

The seemingly innocuous tweet nevertheless set off a wave of ridicule for Donald Trump, the notoriously thin-skinned and boastful U.S. president.

Trump has frequently used Twitter to lash out at his critics in politics, business, the media, entertainment and the world at large. On Sunday, for instance, he criticized the Women's March on D.C. "Why didn't these people vote?" he tweeted. "Celebs hurt cause badly."

He also uses the social media platform to boast about his accomplishments, whether or not they are verifiably true.