The answer is generally yes with rare exceptions.
If the straight buddy is clearly straight, i.e. is married, has a girlfriend/fiancee, this usually works out well. The only case where this might be a problem is if the gay guy gets the idea that the straight friend is in the closet and the gay guy is attracted the straight guy and the gay guy has no compunction about trying to break up the marriage or whatever. Wow, this is a pretty desperate gay guy. That friendship will hit the rocks if the gay guy hits on the straight buddy, but otherwise it should be just fine.
Then there is the case of the unattached straight guy buddy. It’s just the same as the previous except there’s no ‘breaking up the other relationship’ factor. If the gay guy has bad gaydar, especially of the false positive kind, then there might be a problem. Still to resolve this, all the straight guy just has to say is something like, “by the way, I’m straight”. Nothing against a preemptive strike, and so he’s welcome to say so at any time, but he doesn’t really need to unless he’s getting hit on.
Overall, I think gay guys can have straight buddies, and this is a good thing. I mean obviously having friends is a good thing. (And despite sounding very PC, I think having more different kinds of friends challenges one’s thinking a bit more. Probably it makes one think about other points of view, blah, blah, etc, etc.)
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Why doesn’t gaydar always work? You might think gay guys should have really good gaydar.
Gaydar fails not only if it hasn’t been well trained as far as knowing good ‘tells’, but also if it hasn’t been acted on. I think I had extremely bad gaydar in the past, but for a time I tended not to act on it anyway. But after a couple bad false positives where I actually found out: Oh, shit! I was wrong, it improved dramatically. What are the gaydar softspots? There are gaydar confounding signals. For example, the straight guy meets any one or more of the following criteria: (1) wearing tight jeans and an exceptionally well fitting shirt — say the sleeves are cut to show the bicep, (2) maybe the shirt is a light pastel color especially pink, (3) not wearing a shirt and having a well toned upper torso, (4) making unflinching body contact, (5) having a sensitive personality, (6) being very good looking, or (7) maintaining between 4-7 days facial hair growth. It’s difficult for gay guys to get past some of these factors, but it is relatively easy for most straight guys to avoid some or all of them. (1), (2) and (3) might be a problem for straight guys out prowling for women. But if you’re visiting your gay friend, dress down, avoid pastels, and keep your shirt on. If you have an issue with avoiding (4), then are you sure you’re not gay? Perhaps you’re Brazilian or Italian in which case you are excused. (6) is a problem overall here, but come on, if you’re hot — you probably have a lot of women (it’ll be obvious you’re not gay). (7) is easily avoided. (5) alone isn’t much of a risk factor for gaydar errors. But (5) and (6) without a girlfriend is a killer gaydar pitfall. In this case, saying ‘by the way, I’m straight’ is useful. Do it privately though. Don’t feel bad either, you’re helping improve your friend’s gaydar.
I think part of my problem was being unrealistically too optimistic early on. I really hoped that the hot guy was gay — I knew that was unlikely — but then, I tended to think, at least the nice guy might be gay. Probability doesn’t work that way. There are plenty of nice straight guys. I think the key is to develop a healthy skepticism, and then depending on your level of gaydar experience, add even more or less on top of that skepticism.
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Gays shouldn’t need gaydar you say — i.e. it’s obvious I’m straight, and it’s obvious those flamers are gay. This is the claim that it should be easy to determine one’s sexuality based on appearance or actions or statements about previous relationships. Part of this claim is based on fallacy that all gay guys are flamboyantly gay. Even though I am gay, I think many people couldn’t tell based on the way I dress or act whether I’m gay or not. The other part is related to prevalance of the closet. I think there is still a fair percentage of gay guys in the closet today, although it should be going down. Part of the problem is the general assumption which many people make about everyone who doesn’t cross dress being a heterosexual which by default puts most gays in the closet. They have to do work to come out of it every place they go. For lazy, conflict avoiding gay people like myself, it’s a pain.
Of course gay guys aren’t immune to the false positive similarly to straight guys: straight guys might believe a girl is interested in him, if she just flips her hair when surrounded by a bunch of guys and only slightly facing in his direction. Similarly a gay guy with bad gaydar could misinterpret some cue from a straight guy as a sign of interest. There’s an evolutionary reason for this false positive by guys. There’s a practical downside to missing an opportunity to mate, but little more than perhaps embarrassment as a penalty for making the first move and mistaking a no cue for a yes cue. Of course, the penalty could be greater if you’re not in a sexuality appropriate place. I.e. a gay guy hitting on guys in an obvious ‘straight’ bar.