homophobes being somehow closeted or repressed homosexuals.
This is one that pops up way too frequently, including at liberal sites, including this one. As you stated, it is quite obnoxious and, IMO, is homophobic in of itself. It implies, to me, that we are so pathetic as to be unable to accept our own sexuality we, in turn, attack our own, and therefore, homophobia is a problem of the gay community hoisted upon the heterosexual community. It is like claiming racism is the fault of ethnic minorities and its their responsibility to alleviate it. Of course, some homophobia is much more subtle, and, sometimes, gets a pass even from people who claim to be liberals and progressives.
A recent example was the attacks on Glenn Greenwald, making comments about his living situation (younger partner) and referring to him as "GiGi." I can honestly say I don't care for Greenwald, but attacking him because of his sexual orientation or joking about him at the expense of his being gay, is as low as any other form of bigotry. Sure, it isn't as bad as calling him a "faggot," but it isn't really that far off, to me. There are even situations when GLBT rights, issues, and/or concerns are raised, people will minimize it or change the subject in order to mock or distract from those issues.
Thankfully, there are real allies, such as yourself, who realize "fag/dyke" aren't the only ways people are homophobic, and they (allies) take the time to utilize their privilege to educate others.