at Wash U, Pi Phi is paired with Phi Delt every year for homecoming, and with Theta Xi every year for the Thurtene carnival (largest student run carnival in the US)
I couldn't say if any of these were official or not, but on my campus:
AEPhi is always paired with AEPi
DG is paired with Sig Nu
Alpha Phi is paired with Sig Ep
I heard that Chi O is nationally paired with Kappa Sig, but since Chi O is new on our campus this year, and Kappa Sig is paired with Kappa Kappa Gamma, I thikn they are goign to be paired with Beta Theta Pi. Of course everyone has mixers with all the others
Kappa Kappa Gamma and Pi Phi are sister sororities though, since they were both founded at Monmouth college... we have a Monmouth Duo date party together
