I shouldn't admit this, but it actually happened to me.

I was flying between Indianapolis and MSP, I checked the gate assignment after I checked in at security, when I got the gate and even over the entry door, every check showed the gate as being the correct one for MSP. I boarded the plane that Delta indicated was going to MSP (after of course being checked in by Delta team) and when I sat in my seat as we were getting ready to depart they announced the 'short flight to DTW', I panicked. Checked with fellow flyers and we were indeed headed to DTW not MSP. I alerted the FA, was escorted off the plane and then was able to board my correct flight.

Ridiculous but true....perhaps a blonde moment....or as I prefer to think of it ineptitude in signage in every step of the journey.