Couples.
or
Maths for beginners.
.
B+A= a couple of newlyweds looking ecstatically happy most of the time.
.
A+A=two colleagues having a smoke and a drink..
A+B= couple of newly divorced looking for a new BMW.
.
B+A= half of ABBA having fun on stage
.
A+B= other half of ABBA go for the more serious stuff