Dressing for a special occasion can sometimes be a tricky business. There might be some old friends, or important people coming to the venue that might warrant you dress nicely and appropriately for the occasion. It might be possible that a particular function is important from the point of view of business contacts or that you might be looking for a date.
The correct dressing gives a lot out to a stranger about your personality. Even if the person is known to you, everyone forms an impression about the people they are meeting by how they look and carry themselves. Your family members or your close friends might know about your personal qualities and would not judge you on the basis of your appearance or the choice that you make for your wardrobe. This is almost never the case with regular people who are unknown to you.
You might want to wear your floral print shirt or tees when you are heading out to a beach or probably at most when you are going for a poolside lunch post a swimming session but that is probably it when you look at your dressing decisions not so seriously. Even if you are going to the same poolside eatery in the evening, you would want to rethink your dressing approach and might decide to go with some darker shades.
For a more serious group meetup, you may even choose to wear a dark collared shirt with matching trousers and shoes even if you feel like skipping the blazer.
It is anyway a good idea to consider stitched shirts for your meetings as ill-fitted shirts would neither give you the confidence nor land a great impression on others.