Ganging up on Matt Damon! Ben Affleck and his best friend Damon have been hard at work promoting their charity contest benefiting Eastern Congo Initiative and Affleck, however, is giving Damon a hard time for not being on Twitter to help promote the contest -- and Damon's nemesis Jimmy Kimmel has joined in the fun.

"Want to hang with us? Support @EasternCongo & @Water for your chance," Affleck tweeted with a link to his Omaze experience contest with Damon, which gives two lucky fans a chance to hang out with them in Hollywood.

After Kimmel retweeted Affleck's message, the Argo director, 41, asked: "Will Matt and I see you there too in support of these great orgs?"

"I will be there, my darling @BenAffleck," the late night host replied.

".@JimmyKimmel -- I thank you buddy," Affleck responded. "And @eaterncongo & @water thank you! Matt on the other hand? Matt you there? Right. We will fax you."

Kimmel, 46, joked, "Matt is probably too scared to get on twitter because no one likes him."

Twitter CEO Dick Costolo also got in on the Damon Twitter dissing. ".@BenAffleck @jimmykimmel @water we have printed out this tweet and placed it in a suitcase that we will have couriered over to Matt," he quipped.

For more of Affleck poking fun at Damon -- and to find out how you can donate to their organizations -- watch the funny video above!