I usually raunchy and drunken orgy involving anywhere between 3 or more people. A lot more fun than saying gang bang or orgy. Can be used as either a noun or a verb.
A gang bang where you are double teamed by two gorgeous horny sexy blonde twins. This is usually an unattainable fantasy of dirty ugly old men that they will end up having wet dreams about or writing about it in their diaries. The occurence of the schmang twang bang is very rare, but when it does happen it is extremely fucking amazing and orgasms are multiple.
"Damn those twins are so hot, I am getting hard just looking at them, damn I'm tryna have a schmang twang bang"