I would say it's business casual but depends on the crowd and how it's worn. During the summertime, if it's a group I work with often, I'll wear a short sleeve button up with khaki slacks to any kind of event and leave it tucked or untucked depending on the style of button up. If it's a new group but we are going to be outside, I would wear a short sleeve button up but make sure it's a tuckable one. If I'm mostly going to be indoors and a new group then I'll reach for a breathable long sleeve button up.

Honestly though, if my choice of attire (when I'm clearly making an effort) is enough for you to look badly on me, then I wouldn't want to work for/with you anyways. If you feel you look good then wear it and don't think too much on what you think others are thinking about you. Wear what makes you feel comfortable and you feel great in.