When you order a drink from a restaurant, it's a given that it comes with ice, whether it comes in a paper cup or a glass cup. Aside from that jewelry flex, that ice makes the cup very cold. This causes the water vapor molecules in the air surrounding the outside of the cup to condense and become liquid, forming droplets that can drip down the sides of the cup, the operative word here being "drip". This is a flex about fashion sense and having the wealth to dress to impress. Let's be real, there's hardly anyone else in Dragon Ball that can claim to be anywhere near as dripped up as Trunks in any of his appearances, guy wears his mom's jackets and still looks clean.