How do I tell the person interviewing me I’m not longer interested in the job

"Thank you for seeing me and considering me for this job, however at this time I'd like to withdraw my application."

just say oh my look at the time and leave

Say your circumstances have changed, that you appreciate them interviewing you and that you dont want to waste their time.

Call them and tell them you do not want to waste their time or yours, and your just not interested.