Certain items of clothing are completely acceptable when competing yet utterly ridiculous if not. Here's your do's and do not's.
The constant pursuit of perfection has lead to bodysuit swimwear being more prevalent on elite swimmers but the gold standard is still the Speedo. Ideally, less clothes equals less water drag and a faster, frictionless swim. Seeing some of the new 3/4-body suits released in years passed confirms that performance comes first. Those things are ugly.
Outside of competition, the banana hammock is usually reserved for older, perhaps wealthier, most likely hairier, probably European men. Exactly the demographic that most people would rather see with more clothes on than off. Body aesthetics aside, unless you consider tanning a sport, a pair of shorts like Orlebar Brown's Bulldog would be the perfect all day short that allows for plenty of movement for an impromptu beach jog or volleyball match yet still shows enough skin to keep those tan lines in check.
If you run in cold weather, running tights are more necessity than anything else. Though as compression technology has gotten better, athletes across all disciplines have been using them to enhance performance. Evidence from recent studies shows that performance probably isn't enhanced much by these tights but DOMS (Delayed Onset Muscle Soreness, you may not know the acronym but surely you know the pain) can be significantly decreased through compression use. So, whether to ward off the cold or to ward off soreness, tights have a performance based place in your training bag.
Meggings, on the other hand, do not. There's really not much debate here. Skin tight jeans on a punk/hipster/goth/etc is acceptable as long as the denim-to-spandex ration is significantly more denim. MAYBE you could convince me with an outfit based in Ann Demeulemeester or Rick Owens but even then you walk a fine line between ridiculous and fashionable. Despite being used for a whole other type of performance, there is no bonus to wearing these and nothing over them. If you want your fashion and performance in one stretchy bundle, the Nike x Undercover collaboration gives some color and design to the typical black training tights.