A date shanghai is when a person unwittingly goes on a date...whether the person wants to date the other person or not.
'To shanghai' is a term derived from the 1850s when sailing crews were abducted. It is a verb that has expanded to mean to kidnap.
A date shanghai is essentially a surprise (unwanted) date.
"On my last night in town he date shanghaied me! I first realized it was a date, not after the movie in his room or the whiskey shots, but when we were walking to a jazz club. When I invited some people to join us, his face fell a bit. (they didn't join us, so we spent the evening together).