There's plenty of bad language and abuse on social media, but it doesn't usually come from an elected representative in the Australian Parliament.

Libertarian senator David Leyonhjelm has labelled someone a "c---" on Twitter during an argument over Immigration Minister Peter Dutton's text mishap, in which he labelled a female journalist a "mad f---ing witch".

Senator Leyonhjelm, whose profile warns that "offensive abusers are blocked", dropped the "c-bomb" the day after he called another Twitter user a "witch".