I suppose that for the sake of argument, we *could* give it the benefit of the doubt and assume that poster actually *meant* "large", which would be accurate by Merriam-Webster. <sigh>
As for bikinis and having to wear them to prove you are self-confident ... nah. Fashion is one's own preference, and I haven't WANTED to wear a bikini since the Nixon administration, when I was too young to be wise enough to understand that it really looked awful on me.
There are plenty of thin, fit people who just prefer not to wear bikinis, for whatever reason, including caution about too much sun exposure. ((For myself, I definitely wouldn't even if I did feel that they were flattering on me, because I count on having that fabric in the middle to hold my waterproof valuables pouch while I swim. My car keys and credit cards are very happy there, clipped to a ring on the lining of my suit.))
As for men who wear rash guards in the water for whatever reason, why the heck not? If they prefer to dress modestly and/or guard against upper-body sunburn (or like my DS, just the hassle of applying sunblock), why must they "enjoy the sun" bare-chested? (Which gives me an opening to quote my favorite line from
Mulan: "I'll get that arrow, Pretty Boy, and I'll do it with my shirt ON!!

) My Dad was as buff a man as you would ever see, but he wore a shirt in the water (no rash guards back then), on account of having had melanoma; sun wasn't something that was all that good for him.