My biggest regret was selling my 1972 Kawasaki 750 H2 triple. It's a long story, but that bike gave me many years of fun memories.
In 1979, I was working as a technician at the Honda motorcycle dealership in my hometown. That same year American Honda had introduced the Honda CBX six-cylinder engine. It was their flagship motorcycle. It was designed to give Honda bragging rights about the fastest production motorcycle in the late 70's.
In my infinite wisdom, I thought I could purchase the Honda CBX with the measly wages I was making at the dealership. I was so naive, that I gave my bike away for measly $650.00 dollars. Like I said, it was my biggest motorcycle regret in life.