Basic Trope: Someone who sees sexuality in black and white terms, based on a heterosexuality with rigid gender roles for how the man and the woman should be.
Straight: Bob frowns upon homosexuality and other "deviant" activities.
Exaggerated: The above-mentioned "deviant" activities include sex in positions that doesn't look like the woman submitting to the man, or even allowing women to work outside the home. He not only protests a bill that would allow same-sex marriage, but argues that accepting same-sex relationships makes all opposite-sex relationships worthless.
Bob belongs to a religion that believes homosexuality, sadomasochism, and polyamory are sinful, but the most we see of it is Bob referring to MTF transsexuals with male pronouns and looking turned off at the sight of two men kissing in the street.
Bob hates all forms of sexuality, but will tolerate heterosexuality because it "serves a purpose".
Bob has deep-seated issues, such as past sexual abuse, that cause him to think this way.
His past experiences with sexual minorities cause him to stereotype them very negatively.
Bob was raised in a homophobic environment and/or comes from a time of Values Dissonance
Bob believes that anyone and accuses anyone who is heterosexual, homosexual, asexual, a virgin, prefers monogamous relationships, or just isn't that into kinky sex of being a Sour Prude and may even be prejudice against them.
Bob learns in religion class that anything other than a married male-female couple having sex for reproductive purposes is wrong and that he need to fight to "protect" marriage, etc.
Alternatively, Alice give a little speech about the destructiveness of heteronormativity and discrimination, maybe accusing Bob of being a bigot while she's at it.
Defied: Bob makes an active effort to be open-minded about sexuality, gender roles, etc.
Discussed: "Bob, what's with hating the gays?" "It's a disease, Alice. Those filthy sodomites are diseased, and I'm trying to persuade them to seek a cure for their illness."
Conversed: "OK, so this character hates gays. And bisexuals. And bondage. And masturbation." "Is there any sexual contact he likes?" "Well, maybe the kind within religiously-recognized heterosexual marriage for the purpose of reproduction, but only if it's in the missionary position."
Bob may be feeling insecure about his own sexuality, and puts others down (or hurts them) to make himself feel better. This may stem from any number of things, including (but not limited to) his culture and his religion.
Alternatively, Bob has religious beliefs that make him believe homosexuality to be bad but also influence him to "hate the sin but love the sinner". He believe that there is an "the gay agenda" that hurt people by corrupting them into gayness, but that it's best not to target the individuals, just the behavior, but to do it as ethically as possible. Unless he live in a setting where there actually is an evil gay conspiracy, he's a Troubled Sympathetic Bigot.
And, of course, there's always the fact that such kind of people can instigate others to perform terrible deeds for the sake of their crusade, eventually leading to a lose-lose situation for everyone, as the LGBT community ends up as the target of all their atrocities, while the non-radical, genuinelly nice religious people end up taking all the flak for their horrible deeds.