KC AND THE SUNSHINE BAND. BtVS Intertext/Allusion.
In "Faith, Hope & Trick" (Season Three) Cordelia refers to funk/R & B/disco favourites KC and the Sunshine Band to indicate how out of fashion the boy Faith (Slut-O-Rama) is dancing with is. Buffy puns on the word sunshine since the guy is obviously a vampire.
The following dialogue is taken from the Buffy Dialogue Database:
CORDELIA: Check out Slut-O-Rama and her Disco Dave. What was the last thing that guy danced to, KC and the Sunshine Band?
BUFFY: I don't think that guy thrives on sunshine.
KC and the Sunshine Band’s greatest hits were in the 1970s and early 1980s, the track ‘Boogie Shoes’ featured on the soundtrack to the classic disco movie, Saturday Night Fever (John Badham, 1977).
As indicated earlier by Buffy in "Welcome to the Hellmouth" (Season One), vampires can often be spotted by their attachment to clothes that were in fashion when they died.