I remember in the 1950's there were two sides in every licensed premise (now called bars and taverns).  Ladies and escorts on one side, men on the other side. So my suggestion for the $5 bill is a picture of the first  man who went into the ladies and escorts side of the bar, without a lady on his arm, and sat down. Or the first lady that left the ladies and escorts side of the bar and sat down with the men.