Yet again, Donald Trump has blown away our expectations of how far he's willing to go to get attention.

While at a campaign event in South Carolina on Tuesday, Trump decided to read out loud a phone number.

Turns out, according to CBS News, it was the cellphone number of fellow GOP presidential candidate, Sen. Lindsey Graham (R-S.C.).

What Trump did is basically an old-school form of doxxing, an act made popular by the Internet to blast out to the world people's personal information.

Doxxing is a form of harassment. It's serious, and it's also, apparently, in most cases, legal.

“You can post it as long as there is nothing nefarious about it,” LAPD cybercrimes detective Andrew Kleinick told The Daily Beast in 2013. “They are public figures and that kind of thing happens. It’s not right, [but] I know of no crime.”

The exception, Kleinick said, is when it's used to threaten someone, possibly like when so-called journalist Chuck Johnson threatened to release the full identity of a student called "Jackie" at the center of the Rolling Stone-University of Virginia rape controversy.

Trump wasn't necessarily threatening Graham. But it's clear he was trying to retaliate against attacks from Graham, who has been one of the more vocal GOP candidates to call out Trump's ridiculousness. As recently as Tuesday morning, Graham called Trump a "jackass."

"I don't care if he drops out. Stay in the race, just stop being a jackass," Graham said on CBS.

Graham's campaign responded in kind:

Trump's behavior is raising eyebrows, but this isn't even the first time in his month-long campaign that Trump has been accused of doxxing someone. When Univision cancelled his "Miss USA" pageant, he allegedly published a letter on Instagram from Jorge Ramos, the channel's popular anchor, with Ramos's personal cellphone number.

Trump himself has actually been doxxed -- back in a 2013 leak of celebrities' personally identifiable information.

Here's what he told US Weekly about the perpetrators:

"But they've got problems if they get caught … They'll be in big trouble when they get caught – and they will get caught at some point – and they will be in big trouble."

As to whether Trump gets in "big trouble" for his increasingly brash, immature and ludicrous behavior remains to be seen.