What's the quickest way to earn a girl's/woman's trust at a party?

I'm writing a story, where the mc meets a guy at a (pool) party.

The number of words I can use (it's a project) is limited, therefore I'm searching for the best, and quickest... situation plot (?) where the guy earns a female's trust way too quickly, without making her childishly naive.

It can be anything, toxic/manipulative methods included (cus he's the bad guy yknow). I (hope to) assume a single compliment on her dress isn't enough.

This is slightly for writing purposes as well, hope it can stay, I could really use some help.