To quote the Technogirls, a fansubbing group:
Yaoi: shounenai anime (or manga), always of the shoujo classification, in which there is little plot or action except for a sexual encounter between two males, one of which is usually bishounen.
No sign of porn anywhere in there ^^;;
Yaoi is just like anime, another form of art. Some are mild (Song of the Wind and Trees, Gravitation OVA's), while others take a more sexual approach (Boku no Sexual Harrassment, Level C). To affend yaoi anime and manga is to affend any kind of anime, as it is all the same.