driving the tuna bus

the act of performing oral sex on a woman;

Buses have large steering wheels that cause the driver to hold their arms outstretched and somewhat wide apart. This position is similar to the way you hold your arms when bending a woman's legs back to go down on her. Performing oral sex in this position is like driving a bus... the tuna bus.

My room mate walked in on me an my date when I was driving the tuna bus. She was so embarrassed.