Which of the following sexual behaviors is least prevalent among gay men?

A) Fellatio.
B) Oral sex.
C) Anal intercourse.
D) Mutual masturbation.

Anal intercourse is generally less prevalent among gay men compared to other sexual behaviors like fellatio, oral sex (which is synonymous with fellatio in this context), and mutual masturbation. This is because while anal intercourse does occur within the community, the other listed activities are more universally practiced and often seen as less risky in terms of STI transmission.