Manguangua means that something is really easy or made without any considerable effort. Often to refer to someone doing something the easy way because they're lazy.
"Quieren hacer unas elecciones conlos principales candidatos inhabilitados. Que manguangua vale."
"meiguanxi" is a Chinese phrase which means Nothing,never mind,in response to some conditions when other people feel offensive or sorry to you but you don't.
Eg.
-Joe Wong,I'm sorry to broke your glass>_<
-Meiguanxi,I just want to have a new one!