to ride in the middle of the backseat of a car

From STEM, an abbreviation short for "Science, Technology, Engineering and Mathematics", a STEMlord is a pejorative term for a particular kind of person who has studied in these areas at university or works in these fields who holds a pretentious, condescending attitude to anyone who has studied in any other fields, particularly the Arts and Humanities. They typically believe themselves to be more "intelligent" and "rational", while generally remaining incredibly ignorant outside of their areas of expertise and having the charisma of a rotting pig's backside.

Taking the middle position when three passengers are riding in the front row of a car or truck. When two of the passengers are men, the woman sits in the middle to create a buffer, thus avoiding uneeded male-male body contact.When all three passengers are male,Then one is elected to "ride bitch!"