As above,ie directly translated from German as "a man who urinates whilst sitting down"; refers to a man who is hen-pecked or under the thumb of his wife/girlfriend, or is otherwise weak or effeminate.
but fr, peeing standing up doesnt make u manly, loser. it makes u hygienic. plus, its way more comfy not aiming and u can use ur phone. sitzpinklers are here to stay, motherfuckers.