that's racist!: just because you make a joke about a particular race doesn't make you a racist. in fact, the person calling you a racist is probably a racist themselves (ie, thinking it's wrong to say something about black people but that saying things about asians or whites is fine).
that's sexist!: this one is even worse. if you are a guy and don't completely submit to what a woman wants, she will usually call you a sexist or a chauvenist and label you as judgemental and insecure (look who's talking). acknowledging scientifically proven difference between males and females does not make you a sexist, nor does being assertive with a woman or wanting to wear the pants in the family.
you're trolling!: this one comes up a lot recently. if you say anything with a disagreeable tone or even just disagree with what someone else wrote, people instantly assume you're trolling. sure, some people legitimately are, but it's about intention, not opinion. real discussion is going to have disagreaments and perhaps emotional conviction, this is not the same as deliberately going to a thread and posting hate comments for their own sake
go green: this is the cheesiest and most ridiculous sounding guilt trip ploy I've ever come across to get people to buy "green" products. I have no idea how people regurgitate these kinds of slogans without realizing how brainwashed and silly they sound.
if people could just
1) think for themselves
2) actually listen to what people are saying
3) not assume the worst possible connotation of what someone says
4) not be so easily offended, especially about things that have nothing to do with them
we could easily avoid such ridiculous overused jargon and have real conversations with people