David Einhorn speaking at the 24th Annual Sohn Investment Conference in New York, on May 6, 2019.

At the Sohn Investment Conference in Manhattan on Monday, Greenlight Capital founder and president David Einhorn said Tesla CEO Elon Musk's promises about Tesla's self-driving vehicles amounted to "a lot of horse---t."

Greenlight is famously short shares in the electric car maker, and Einhorn is regarded as one of the most prominent and vocal critics of Musk as well.

Last year, Einhorn and Musk clashed over Greenlight's short position in 2018, after the hedge fund suffered losses from Tesla's rising share price in the second quarter. After that clash, Musk fans at Chubbies, a mens' apparel business, sent a box of short-shorts to Einhorn.