Trump held his hands out, arguing there was nothing small about them. 
He then took on the implicit jab from Rubio directly. 
"I have to say this: He hit my hands. Nobody has ever hit my hands. I've never heard of this one. Look at those hands — are they small hands?" Trump said Thursday recalling Rubio's recent barb.
"He referred to my hands — if they are small, something else must be small. I guarantee you, there's no problem."
The remark provoked applause and laughs from the crowd and created an instant firestorm on Twitter.

Rubio's comments came on Sunday.
“He’s always calling me ‘Little Marco.’ I admit, he’s taller than me; he’s like 6’2”,” Rubio said Sunday in Virginia as the crowd roared. 
“Which is why I don’t understand why his hands are the size of someone who is 5’2”. You know what they say about men with small hands? You can’t trust them.”