It’s not really a rule, just a pet theory Sedaris had, which he freely admits he found exceptions to, including straight men to whom it was all about the dessert; they would eat frosting off another man’s penis if that was the way it was being served.
Penis cake?
“Will fuck for dessert.”
Not quite the same as “will work for food.” 
Ditto…but if you tried to get half of a fork or spoon full from my SO’s plate, there will most likely be a fork or knife through your hand…he loves dessert (and is skinny) and doesn’t like to share much.
Quite seriously…I split a large cookie (somewhat unfairly) with him back in 1997 and have still not heard the end of it.
To respond to the OP:
Straight man; I’d share a dessert that wasn’t composed of discrete items with my wife, my son, or maybe my sisters (don’t have any brothers). That’s about it.
I ain’t sharing dessert with no one. Get your own motherfucker.
Actually, it’s not gay if your spoons don’t touch.
For me it definitely becomes gay if one guy’s spoon goes in the other guy’s mouth. That’s definitely gay. Spoons touching gets close, though.
Amazing what a comma can do, I had no idea a motherfucker was a kind of desert! :eek:
MINE.
Straight male here.
I almost never have dessert; even more rarely, in a restaurant. But if my male friend wanted to have dessert, and wanted to share it with me, I’d gladly give it a taste. Depending on the friend, hygiene/sanitation issues may come into play but… really, how homophobic do you have to be to think something like that would make a person gay? :rolleyes:
As long as it is not a fudge covered banana split, I would do it. Who cares? It depends on the person more than anything. I have seen my best friend since childhood do absolutely everything even as an adult and I mean that literally. Dessert sharing wouldn’t even blip the radar. If it is some random guy in a truck-stop somewhere, it might give me pause especially if the dessert didn’t look fabulous.
I never had strong inhibitions about sharing food or drinks with seemingly healthy people of any stripe. Hangups about that are more fruity than any dessert a Parisian chef can whip up.
I love David Sedaris and his sister, Amy! Anyway, I’m a straight woman who will share dessert with any human being. If I notice two men sharing a dessert, I’ll probably assume they’re a couple. I couldn’t care less if you’re gay or straight though. My assumption - I’m not sure - has probably to do with stereotypes of straight men rather then gay men.
I’d have no problem sharing with a guy but it’s never come up. If I get dessert at all, I’m with a woman who wants dessert but feels guilty unless we split it (meaning I take a token forkful), or can’t decide between two choices so I order one of her picks so she can sample both (and get a token forkful). I’ve never been out with a guy or guys that wanted dessert.
I don’t think anyone is seriously saying sharing a dessert with a man turns someone gay. I certainly wasn’t but it just isn’t something I would do. It wouldn’t even occur to me to do it. Thus making this an interesting sociological question.
Do you know the difference between tiramisu & a BJ?
[spoiler]No?
Wanna go get some Tiramisu? :D[/spoiler]
Special snowflake (celibate/not sure/moot) and dessert is mine, all mine.
Straight female and almost always share. Not because the desserts are too big but because I usually can’t make up my mind what I want, so a friend and I order two different desserts and have half each of each one.
But we do divvy them up first - no eating off anyone else’s plate.
I, too, read The Onion. 
The way you do it, to show you don’t have TEH GHEYS (if you’re straight guys, or a guy and a girl who are just friends) is
A) make sure you have a second plate
B) one person cuts/scoops/divides the dessert in half, dumping that half on the spare plate.
C) the person who did NOT do the dividing gets to pick which portion they want. Each eats separately.
Only people in love* scoop a dessert from the same bowl/plate.
I have spoken.
*or, occasionally a grandma who says “I just want to have a tiny taste–just a smidgen. I’m not hungry enough for a whole dessert on my own but it looks so good. You don’t mind if I take one little bit, do you? You won’t even notice it” and then proceeds to devour 7/8ths of the dessert. That said, grandmas have this right. It’s in the Constitution, the Magna Carta and the Bible.