A homophobe is anyone who has an irrational fear for homosexuality whether they are aware of this fear or not. Since prejudice of any form is irrational and a product of fear of difference anyone prejudiced against homosexuals is homophobic. Some homophobes maintain they are not homophobic because they don't mind homosexuality but they wish the would do it behind closed doors/not kiss in public/have no equality/have no freedom of speech/would just go away. Again, this is an irrational treatment of homosexuality based on prejudice: at least do the honorable thing and admit you are a homophobe.

euphemistic drift for the semantic elite: The word homophobe was created by joining "homosexual" with the root "phobic" for "illogical fear". This is understandable as "homosexual" is the only word a given slack-jawed yokel might know with this prefix, but it is as etymologically twisted as the word mathematics.

The prefix of "homosexual" is not the Latin "homo-" meaning human. (Otherwise "homosexual" would mean "human-sexual" or "bisexual" and "heterosexual" would mean "other-than-human-sexual". Bestiality?) No, the root is the New Latin "hom-" or "homos-", meaning "same." Károly Mária Kertbeny first coined the term homosexual in the late 19th century as a neutral term to distinguish between people who were sexual with the other "hetero-" gender, from people who were sexual with the same "hom-" gender.

In either case, "Homophobe" would mean "fear of humans" or "fear of what is the same," neither of which fits its actual usage.

As pointed out by Tato the word is etymologically nonsensical. Also, it is a little presumptous to say that the quintessential anti-gay macho man gay bashes because he's really afraid of them: there's all sorts of reasons to hate another human, only one of which is fear. A couple of alternatives that really intellectual people might use are:

Heteronormative, that is, people who hold that there is something "unnatural" about same sex relations; and

Heterosexism, since homosexuality can be considered a discrete gender and a person prejudice against a gender is a sexist, a heterosexist is someone who is favorably biased toward the heterosexual genders (male and female).