When you feel an impulse to talk or joke about physical appearance, politics, religion, sex, gender, rape, racial issues, nationality/ethnicity, etc., just hold your tongue!
Going to such extremes to guarantee never offending anyone is a great way to wind up unhappy and alone at work. It's fine if that's what you want - when I don't like talking to my coworkers in the first place I happily implement that strategy.
Chances are that anyone using that strategy and isn't also miserable has a fair number of unspoken assumptions about acceptable behavior, and isn't actually using that strategy. They're just slightly more guarded than in their normal behavior.