As someone on the other side of the table, if someone doesn't feel an interview is going well (either because they can see they aren't going to get hired or because they don't think they would accept even if they were offered), I want you to politely tell us something along the lines of "I'm sorry, but I don't believe this is the best fit for either of us. I appreciate the chance, but I think we should end it here." Each side shakes hands with a smile, and we go on our own ways. In the end, it's a waste of your time and our time if either side has already made up their mind. We, the interviewers, end interviews early semi-frequently (for example, if one is going poorly we will just skip a coding test). There's no reason the interviewee can't do the same.
Just be polite about it. Don't burn any bridges. You never know when the other interviewers (the ones who stayed in your case) will be interviewing you at another company and remember you for leaving a bad taste in their mouth.
Just be polite about it. Don't burn any bridges. You never know when the other interviewers (the ones who stayed in your case) will be interviewing you at another company and remember you for leaving a bad taste in their mouth.