Your argument is basically akin to saying that, because I told some dirty jokes to my friends in private, I'm never allowed to complain when someone tells a dirty joke in public.
Ah, Twitter is now considered private but two devs speaking in their chairs are pretty much delivering a speech.
Besides, you're putting words in my mouth. I never said you're not allowed to do these things, but you shouldn't be allowed to complain about it, just like senators who watch porn lose credibility when passing laws against all forms of porn.
There's also a matter of context. A personal twitter stream is a very different context than a professional event. If I'm friends with my coworkers, I may hang out with them after work, and a dirty joke then is perfectly acceptable. But with the exact same people, at the workplace, a dirty joke is inappropriate. Exact same people. The difference is context.
Furthermore, you wouldn't then see yourself as a "hero" for publicly shaming the people who made said lewd joke. Simply turning around and telling them that what they're doing isn't appropriate.
Also, it's not like those two developers were using a microphone or loudspeaker or some such device, they were just chatting away behind her and talking to each other. Sometimes we forget that people may overhear us when we talk to each other in a public setting. In that context is inappropriate speech(not sexist, not outright wrong, just inappropriate for that context) grounds for public shaming and firing when you simply could've forgotten(or not thought about) being overheard?
I just think that she went overboard with the reaction and even seeing herself as heroic for doing something like that. The fact that she makes jokes like that in a different context simply shows that it couldn't have been that offensive to her(maybe just cringe-worthy) to warrant such a reaction.
(wikipedia article on ad hominem)
In this case, i'd think it's pretty fucking valid.
Argumentum ad verecundiam fallacy (argument from authority), supporting argumentum ad hominem fallacy.
Nicely done.