a) everything and anything. So basically, the word can be good or bad any way you say it. It depends how you say the word. if you say it angrily, it can be like a weaker or stronger replacement for FUCK. It can also be 'Oh My God!'. We don't care. Use it wisely.
b) when talking about a person, the person who is a gehig (in this case a bitch, fucker, shithead, whore, slut, douche, ect..) should be called a gehigger.
To a person: What a gehigger!