A rainy day couldn’t keep the crowds away from Tango Night in Allston, a music and dance event organized by the Harvard Ed Portal and the American Repertory Theater (A.R.T.) and featuring the Argentine band from the A.R.T.’s current production “Arrabal.” Instructors from Brighton-based dance studio Artango led over 200 attendees in a tango lesson, and then the band took the stage to perform a set while the audience danced along. After what was supposed to be the last song of the evening, cries of “¡Otra, otra, otra!” filled the room and the band returned for one more number.