Vacilar is a fantastic slang word with many meanings depending on the context! While it can literally mean 'to hesitate', in many parts of Latin America it means to party, to tease someone, or to show off.
In 'Que Tire Pa Lante', when Daddy Yankee says 'me gusta como vacilas', he's saying 'I like the way you move/party/show off'. He's captivated by her confident and playful energy on the dance floor. It's a perfect word to describe the fun, carefree vibe of reggaeton.
Daddy Yankee brings pure, direct dancefloor energy in this track, throwing down a challenge from the very first line: "Tú eres atrevida / Hablaste mucho pero no tienes salida / Ahora demuéstrame" ("You are bold / You talked a lot but you have no way out / Now prove it to me"). The phrase "Que tire pa'lante" comes from Caribbean Spanish, a shortened version of para adelante, meaning "step up" or "bring it on." He isn't looking for romance or drama ("aquí no andamos en sentimiento" / "we are not into feelings here"); he just wants to see who actually has the moves to back up their talk.
The lyrics are packed with fast, cocky punchlines and clever wordplay. He compares his crew's unstoppable pace to a high-speed car ("Flow Ferrari que rompe la calle" / "Ferrari flow that breaks the street") and drops a funny sports brand pun when describing the crowd watching his partner: "Esta gente parecían tennis, los tenías haciendo FILA" ("These people looked like sneakers, you had them waiting in line," playing on the sneaker brand Fila and the Spanish word fila for a physical queue). By the end, the competition is totally rigged in his favor anyway: "Si ganas yo me voy contigo / Si pierdes tú te vas conmigo" ("If you win, I go with you / If you lose, you come with me"). Win or lose, nobody is leaving the club alone.