I think there are degrees. It all depends on the quality of the sex and the frequency with which you can obtain it, in relation to how you and others value your participation in a given social situation.
Significant other sex is generally not considered a good enough excuse for missing even minor social events, though it is a good excuse for being late once in awhile. Missing an social gathering because of sex with a S.O. can only be justified via rare liberating events, such as an uptight girlfriend agreeing to do anal or participate in a threesome.
For most situations, consider the Bar:
If you ditch a friend in a bar to go have vanilla sex with a hookup, then you are ok. If you ditch a friend in the bar to go have vanilla sex with your boyfriend, then you are a jerk. Wild-monkey-sex with a significant other is an acceptable excuse if, when next you see the ditched friend, you show them evidence of heretofore unknown sexual adventurousness on the part of your S.O. such as scratches, bruises, or flaming holes-in-the-wall.
(remember, it's all about degree here)
"The Bar" rules may also be applied to missing all non-major social gatherings, such as PTA meetings, bowling night, and non-playoff sporting events.
For major life events:
If you miss a friend's birthday, wedding, or other major event - for sex - then it had better be your one chance to get with someone you've had a crush on since middle school, a celebrity of "B List" quality or higher, (no local bands, reality tv stars, or your small-town mayor) or a similarly novel partner, such as a mutual friend's mother or a midget. If you shag your husband, regular fuck buddy, or a friendly homeless person thinking it will get you out of going to your best friend's sister's wedding, you have committed a faux pas and must make amends.
"But 26", you ask, "what if I'm a total slut/stud who gets with supermodels every weekend?"
The main thing to remember here is that as long as the sex you have while you miss your commitment differs in degree significantly from the sex you have on a regular basis, you should be in the clear. In the case of individuals such as this though, it becomes a challenge.
Sex with a sitting head of state, or a marriageable billionaire, sex on a spacecraft, the pitcher's mound at Wrigley field, or sex in the Vatican, or some combination thereof will get you off the hook. But let's face it, your friends already hate you because you get it more often than they do, without any apparent effort, so the story had better be good, you cheeky bastard.
P.S.
I agree with the above posters who think "bros before hos" is a perfectly acceptable colloquialism in this context. I never thought a site dedicated to letting it all hang out would have so many uptight folks on it, but this place is more sensitive than my cock sometimes. Remember, it's all about degree.
If I'm out with the fellas and one gets a booty callor meets a chick that wants to fuck, we'd talk trash about him if he chose to hang out with us as opposed to going and handling his business. I've ditched and I have been ditched but for my circle of friends sex is always a good cause. No one takes it seriously and no one's feelings are hurt.
