The diver Tom Daley posted a video on YouTube in which he told his viewers that he has a boyfriend (if he made any more revelations in the last minute or so, I missed them because I stopped watching - he doesn't half go on). Some delightful person called RogerGT posted a comment saying 'Of course he's gay! He has a sibilant 's'.':
More to the point, though, is that everyone's 's' is sibilant: that's the term for that particular type of 'hissing' sound. 'S', as normally pronounced, is the canonical example of a sibilant. So, not a good diagnostic for someone's sexuality then.
What RogerGT is probably referring to is the camp stereotype of 'lisping': producing a sound more like 'th' /θ/ instead of 's' /s/. Daley does actually do this a tiny bit, though I'd never noticed it before I went back and listened out for it.
So what have we learnt today? Well, from a linguistic point of view, we've learnt that people are quick to stereotype or judge people based on their accent, that people don't use linguistic terminology right (jk we all knew that already), and that people are really extraordinarily good at spotting even tiny differences in the production of speech sounds.