Dunn died in a car crash in Pennsylvania on Monday morning (20Jun11), leaving his Jackass castmates devastated,
The star was said to have posted pictures on the internet of him drinking with pals just hours before the fatal smash.
Ebert took to his Twitter.com page after learning of the tragedy, posting, "Friends don't let jackasses drink and drive."
Margera had remained silent about his pal's death, but after learning of Ebert's remark, he's hit back at the writer - and expressed his grief at Dunn's passing.
In a series of posts on his own page on the microblogging site, he rages, "I just lost my best friend, I have been crying hysterical for a full day and piece of s**t Roger Ebert has the gall to put in his 2 cents.
"Millions of people are crying right now, shut your fat f**king mouth!"