Look you’re going for: Like you understand that "casual" is a good look and "sweaty" is not
Taking a girl to a party on a first date could be considered sketchy on a lot of fronts, but when you have mutual friends and you'll both know people there, it's a great way to see how you get along in those types of situations with friends around. The heat will be on, though—literally and figuratively—and you don't want to funk up the date. Making sure that your clothing is breathable is key, so a plain T-shirt is a good, especially a dark blue one that will hide potential pit stains but won't attract as much heat as a black one would. Shorts are always dicey because too much man-thigh is enough to make anyone question a man's motive, but if you have a pair that sits right above the knee in a cool pattern to complement the tee, it could indicate that you're fun, but don't go overboard. Stay away from the flip-flops and opt for some slip-ons to complete the look that will keep you hot with your date while staying cool as the heat beats on the rooftop.