Swear words, definitely. Never got why certain synonyms of otherwise benign words were somehow bad. Even if they can be used in a derogatory way, the words themselves aren't bad, it's the context.
Being open about sex and sexuality in general, straight or otherwise. I mean yeah, in certain company it'd be TMI to talk about sex stuff but sex is a normal biological function. In fact I'd extend this to any natural function or bodily thing, like illness (physiological or mental), miscarriage, etc.
Actually, I want to extend even further, to human feelings that aren't quite "taboo" per se but seem to be discouraged in our society from being expressed, particularly in social media and the internet in general. Online we're kind of pressured, if unconsciously, to portray only our best side, and hide things like loneliness, sadness, envy, and other negative emotions for fear of appearing like attention-seeking whiners or just negative in general, and if you're trying to market yourself professionally via the internet, you have to be extra careful. And if you don't have many trusted people to share these things with, it can be very isolating and heavy indeed. However, these feelings are just as much a part of the human experience as feelings of success and togetherness that we see more often in our feeds. This, at least for me, breeds feelings of inadequacy and makes me feel even more distanced, even though I know deep down that all those people are also human and probably feel the same way. Can we not all just be human?