A quote from Bokura ga Ita:

Takahashi(the girl) and Yano(the boy) are about to sleep together for the first time.
takahashi is really nervous though and wont take off her clothes.so Yano comforts her and says:

"dont worry takahashi. just imagine: we are on the beach,the waves rolling,and look! see? i'm in my swim shorts! now,Takahashi,show me your bikini!"