I'm sure that must be very hurtful. But I wouldn't even think that you should change therapists just due to a one-time thing like this. I also don't think your therapist was trying to do anything. Sometimes people laugh at inappropriate times, due to nerves, surprise, etc, without meaning any harm. Therapists are train to be more emotionally grounded, but can still make mistakes. The most healing thing is often not avoiding mistakes so much as repairing the hurt within the relationship. So my suggestion is to talk about it, even though it may be hard at first. If you don't, your therapist may have no idea how you feel, but if you do and the therapeutic relationship is a good one, you may find it a healing experience to talk through it. Just an idea. I'm really sorry this happened to you though.