United States billionaire Elon Musk has a long history of opinionated quips on Twitter, and his most recent squabble saw the Tesla CEO facing off with U.S. Sen. Bernie Sanders over the wealthy paying their "fair share" of taxes.

After Sanders tweeted with a "demand that the extremely wealthy pay their fair share" of tax, Musk threw some shade in return.

"I keep forgetting that you're still alive," the 50-year-old Tesla mogul clapped back in a tweet to the 80-year-old democratic socialist congressman. "Want me to sell more stock, Bernie? Just say the word."

Musk had just come off of selling nearly $7 billion worth of stock in the company he founded after asking his 62.5 million Twitter followers whether he should sell 10% of his shares. He received a resounding yes.

He sold $5 billion of it after the poll earlier that week and then another $1 billion that Friday, mainly to make a point about the proposed "billionaires' tax" being touted by congressional Democrats.

A week ago, Musk explained on Twitter that he doesn't earn a cash salary or bonus. "I only have stock, thus the only way for me to pay taxes is to sell stock," he said. To earn the income that would be tax-eligible, he offered to sell the 10%.

Just seven hours after he asked on Twitter, his poll had received almost 2 million responses, with 55% approving his sale proposal, Reuters reported last week.

The stock sale didn't stop activist and former Sanders' staffer Melissa Byrne from defending her former employer with the tweeted words, "Folks, quit buying Tesla. Don't reward abusive men."