To be perfectly honest his behaviour sounds inappropriate - im suprised that no other group member noticed what he was doing and more to the point did the group leader do anything to try and resolve the issue? Its not fair that you should have to give up DBT because of this person - groups are meant to be safe and strictly controlled. I would also tell your T if you can that you found her to be invalidating and that the sitaution is serious because its making you want to quit the programme. Maybe your T can liaise with the group leader? Maybe write a note to the group leader if you feel you can't talk to them. Im sorry you're experiencing this - no one should be made to feel this uncomfortable. Are there different DBT groups you can attend? sometimes when the number of people attending is so large they seperate people up into different groups so maybe you can switch? I hope you manage to get this issue sorted out, don't give up on all your hard work otherwise this person wins - that is of course, if they know that what they're doing is damaging, as the poster mentioned above, this person may not realise the effect they're having and all it could take is a quick discussion with him. Please keep us updated, all the best.