Viall, 36, replied on social media to a long stream of unflattering Shatner posts with a simple sad-face emoticon on Tuesday.
The Star Trek actor had fired off numerous messages on Twitter criticizing the Season 21 The Bachelor star beginning on Monday night.
Even before Dancing with the Stars debuted at 8PM ET/PT, Shatner tweeted, "My goal for #DWTS is to knock Bachelor Nick out ASAP. Who is with me? Whoever your favorite is - just not Nick - make the 10 phone calls for them."
And Shatner, 86, definitely didn't stop there once the show began airing.
"How do we get #BachelorNation to not vote for Nick?" wrote Shatner, who co-starred on NBC's Better Late Than Never reality series last summer.
"Keep voting #DWTS Don't vote 4 Nick #BachelorNation."
When a fan tweeted that Viall should win Dancing with the Stars so he doesn't return on a future season -- a joke referencing Viall's multiple failed attempts at finding love on two seasons of The Bachelorette and one season of Bachelor in Paradise, which finally led to an engagement to Vanessa Grimaldi on The Bachelor -- Shatner replied, "No! He needs to go next week."
Shatner didn't exactly reveal why he has it out for Viall, but it's clear he's a frequent The Bachelor franchise viewer.
"He lives up to the homonym of his last name," Shatner told a fan of Viall when asked why he dislikes the guy so much. (Viall sounds like the word vile).
Replying to another confused fan, Shatner tweeted, "Watch [Andi Dorfman]'s Bachelorette Season where he started this Viall journey."
Some people naturally supported Viall against Shatner's attacks, with one person writing that he deserves another chance.
"Leopards don't change their spots," Shatner disagreed on Twitter. "Don't be surprised if he shows up again on Paradise. I won't be."
Shatner's "paradise" comment would seem to suggest the actor believes Viall's engagement to Grimaldi will not last. Some could also argue Shatner was insinuating that Viall has the wrong intentions and just loves being on television.
Shatner, who admitted he's "awful-ly determined" to get Viall kicked off Dancing with the Stars, even asked his followers for "an early birthday present" -- "Don't vote Nick."
The Star Trek alum additionally wrote the following message to Murgatroyd: "@PetaMurgatroyd Peta, you know I love you. Congratulations on becoming a mommy. Just can't cheer you on this season. Love to Maks & [Shai]," calling out her fiance Maksim Chmerkovskiy and son Shai Aleksander.
Murgatroyd, similar to Viall's reaction, tweeted back at Shatner with only three crying-face emotions.
On Monday night's Dancing with the Stars Season 24 premiere, Viall and Murgatroyd earned 24 out of 40 points for their cha cha routine from the judges and therefore tied for seventh place with another couple on the leaderboard.