A hollow, plastic, toilet-shaped box, which is often used on camping trips. It is a portable chamber pot. You should not pee in a groover, because then, the pee will slosh around inside it while you travel.
"Who peed in the groover, I have groover juice all over my bag!"
A more contemporary version of the 17th and 18th century term, "Fop". A groover is someone who finds themselves exceedingly stylish or hip, to the extent that those around them regard them as foolish or goofy.
That girl/guy thinks they are so hot, but she/he's like sixty and wearing pleather, man, she/he is a total groover.