If it happened so, that you have an old oversize tee, which is used quite rarely, then why don't you just customize it the way you want? So, let's personalize your old oversize t-shirts to make them look beautiful and statement. Try some cool beadings ro instance, like modern embroideries, just opt for a basic pattern, like tiny stars, which will look cool and modern. Or you can spice up the back of your top, making it creative, by opting some simple patterned slits. If you still wondering how to underline your uniqueness, then you can always take scissors and trim the arms, or you can simply roll up the sleeves and make it look boyish and tough tomboy. If the body of your shirt is quite short, then you can wear it off the shoulder, if the collar is quite small, then you can use scissors to carefully cut it from the point of one shoulder to the other point. We love this retro 1980's inspired shirt.
If you want something more modern, like the 1990's look, then you can make your t-shirt a bit cropped thanks to the scissors cut it where you want.