British Naval lingo for marines, IE "GROund POunders." Same contraction also used in the science fiction series Babylon 5: GroPos; Ground Pounders.
Also the name of a KAOS robot from the 1960's television series Get Smart
Gropo has nothing... zero to do with 'groping'.
kind of like groping, or stroking. or just touching sexually.
a man or a woman who looks like they might rape you.
"what a gropo man. hurry run away fast!"
"in moulin rouge, the duke and his hat. he was groping his hat. so he's a gropo."