A graphic tee shirt is one of the best ways to express your individuality when the temperature is high and your will power to put together an outfit is low. I rarely wear a shirt with a verbal message on it unless I thoroughly believe in the message. I see shirts all of the time with messages like 'begging for the weekend to start'. Although I do love my weekends, I value each and every day/waking moment like the rest of society values on the weekend – so I don't wear 'those' shirts.
The most casual and final way to wear white denim is with a tee shirt and a casual shoe (Toms, sandals, or even Sperry Top-Siders if that's your cup of tea). You can go with either a plain v-neck/crew neck shirt or a graphic tee. The tip of the day is to basically watch what you wear on your chest.
I support all forms of self expression through fashion, which is why you'll never catch me bashing or shaming what someone's wearing; just be aware of the image you want to give the person you might meet or run into when you're wearing that shirt.