Vergo went with his left leg, and then in the middle of it switched to the right leg. It would align with Vergo's inherent and interwoven characterization of being somewhat of a joker, a parody on the underworld name of his boss and close friend Doflamingo. I for one can see this being true, Vergo wanted to get a chuckle or two and trolled Judge's son like that. There's also Vergo's nihilistic outlook, which is deftly woven into his characterization - his personal philosophy draws heavily from
Narodnaya Volya literature, for instance. That and Vergo's running gag of things being on the wrong place, like food on his face, which itself is a cryptic reference to Turgenev's Russian epic
Fathers and Sons, would suggest this to be the case.
Oda also clarified it in an SBS
A bigger version