Mitt Romney is interjecting a bit of humor into his criticism of Republican presidential front-runner Donald TrumpDonald TrumpWH adviser Stephen Miller: 'Nothing wrong' with Trump travel order Mellman: Rating the presidents Webb: The future of conservatism MORE
 
Romney appeared on "Jimmy Kimmel Live" on Tuesday night, during which he read a series of mean tweets aimed at him from Trump supporters.
 
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Romney read a tweet from Trump himself criticizing the 2012 GOP nominee for losing and noting that another rival who challenged Trump this year, Sen. Lindsey GrahamLindsey GrahamCheney to intro Pence at Jewish GOP event CEOs come to defense of border tax plan Trump’s feud with the press in the spotlight MORE (R-S.C.), "got ZERO" and dropped out.
 
"Got zero? The only people I know who got zero are the ones who paid $25,000 to be at Trump University," Romney quipped.
 
A tweet from a Trump supporter asked where the former Massachusetts governor buys "the shoe polish" for his hair. Romney joked, "I buy it at Costco in bulk."
 
Trump responded to the jokes Wednesday morning, sarcastically labeling Romney a "wise guy."
 
"He should be trying to unify the party, not tearing the party apart," Trump said on "Fox and Friends" after Romney's speech last week ripping Trump, which polling suggests may have backfired.
 
"Instead of fighting it, they should be embracing it," Trump said of his critics in the GOP establishment.