I find that I can cope with student inattention, misunderstanding, or laziness effectively. What I find most difficult is student unkindness.
Some students come to college with an immature view of professors. Typical of middle-school children -- truthfully, even more typical of toddlers -- these students see themselves standing for their personal dignity against the authority figure rather than as adults who are in class to learn something that they themselves have decided they need. These students are unkind, rude, undermining, and distracting. Their snide jokes tend to draw others into their disruptions because they relate to the others as heroes on their side. Whatever the professor is trying to accomplish in class, these students will take every opportunity to treat the professor as an inept outsider.
Because I extend myself to set up an atmosphere of courtesy and friendliness in the classroom, my response to rudeness has not been to call it out, but to squelch its effects by passing it over as unimportant. If I call the rudeness out directly, students like the ones I describe will take it as an opportunity for argument. The attention now being centered on them, they don't care if their grades go down. It has been more effective for me to diminish trial rudeness by ignoring it; normally it disappears.
Unfortunately, (and, fortunately, rarely), there is the occasional student who has not matured beyond toddler or middle-school level emotionally. These students have to be directly punished and possibly expelled from the class. It's depressing because I know they are harming themselves. Nonetheless, it has to be done, because other students' learning and my own progression through the course are not to be hindered.