Once in awhile, a patient will preface what they are going to say by saying "I hope this isn't TMI [too much information]." There is no such thing as TMI for your therapist.
It used to be common knowledge that patients in therapy were supposed to discuss all of their thoughts, feelings and experiences. Dreams and sexual fantasies were common topics in therapy sessions. Of course, most people are not comfortable immediately discussing their most personal thoughts, which is fine. Most people begin by talking about what is going wrong in their life. It's important for the therapist to know more than the superficial details, however. Patients who hide details of what they consider embarrassing material may be leaving out important information.
Sometimes people hide information out of fear. A drug addict who doesn't really want to give up drug use may hide the extent of his/her use in order to avoid confrontation and a referral to an inpatient facility. It's important to trust that the advice a therapist gives is based on clinicial evaluation, not judgment.
I've had some patients who apologized for cursing in sessions. If you feel like cursing to express yourself, go ahead (if you feel like cursing at me, however, I suggest we discuss what is making you angry instead).
The basic rules of social interaction mostly don't apply in therapy sessions, the exceptions being that you are supposed to be on time, pay any bill that you owe, and participate. Cursing, talking about sexual behaviors or fantasies and admitting to drug and alcohol use fall into the realm of expression. Without your honest expressions, therapy cannot be effective.