You have a strong insistence on decorum/propriety. Or as psychologists might measure it, a 9th decile of Agreeability. This is a good trait, but not everybody deserves it.

In my life I've found that the more genuine and supportive friends I have around me, the easier it is to chase away the constant fear of isolation.

Some of it is a matter of habituation. You won't go straight to "making a scene" without having a bit of experience contesting things and asserting yourself at lower stakes. Everything has to be built up; it's very rare that a full-fledged capacity appears out of nowhere.

At a certain point the anger makes the long-term consequences blur into the background.

same.. when people go off on screeds during lunch at work telling everyone how america is the best country on earth and how the banking system we have is the best system anyone has ever come up with i silently tune out instead of going off on them.. mostly because everyone thinks im a complete idiot, and that makes me feel like if i speak up they're only going to believe what they believe even more

Go find some theater kids, they WILL show you the way.

You feel the fear and you keep moving despite it. That's how.

Don't get me wrong, it took me a long time and the loss of a lot of fucks to be able to just say what I thought at any given moment.

This is an important question and I wish I had a good answer, because I can think of at least one occasion where I should've made a scene but was afraid to do so (although mostly for long term consequences rather than short term discomfort). For opsec reasons I won't be too specific, but some strangers came to promote an extremely ghoulish opportunity for a course I was taking, involving a live presentation and a question session. In an ideal world I would've quickly used that question session to publicly ask how the people promoting this event could sleep at night, why they felt comfortable promoting violence to a young and impressionable audience, if they understood their role in the world as oppressors, etc etc (this wasn't military recruitment but along the same vein). I didn't say anything, and I think back to the rage that I was feeling in that exact moment and I honestly really wonder what I would've said if I did commit to starting a scene. For what it's worth, I've started several scenes since that day, and have lost favor with several people over it. I've also met a handful of allies doing it, which has turned me into much more of an optimist because you never expect people to agree with you when you're the guy making a scene over stuff most people see as normal

Maybe the critical thing is to practice a bit of revolutionary (social) suicide. Knowing what we know and believing what we believe is already gonna alienate people. That's something we need to be cognizant of because it's a basic reality of being a politicized and radical individual within a complacent and stagnating society. But to start to turn the engine and turn your belief into material change, you have to accept that it comes with a cost to your own image socially, and it will make people think you're mentally ill for thinking that starving children to death is wrong, or thinking that burning down the Amazon is not an acceptable price to pay for a 2% increase in quarterly earnings for an agrobusiness corporation you've never heard of. Accept that preemptively, but also, assume that lots of people already feel just as uncomfortable with the thing you're starting a scene about, as there are people uncomfortable about the disturbance.

I always look at it as taking the social brunt for the sake of other people who don't want to act up.

I'd ask questions I knew the answer to in my courses because I figure that if I found it kinda vague, there's probably at least one person who didn't follow and I'm helping them.

Likewise, if I feel the need to speak up, there's a chance there's someone like you who wants to, so I do it in their stead.

Look for opportunities to make a small scene or even a tiny scene, once you’ve made a million little microscopic scenes you might feel confident enough to make a moderate one. Hint: might not work (I haven’t tried).

Dunno really, the only time I've ever successfully made a scene was when i prepared mentally and studied for it.

had the caring what other people think bullied out of me. was not worth do not recommend

What are you thinking of when you say, "make a scene"? Is it you as an individual doing something alone or are you thinking of organizing a collective action? I would recommend doing the latter. And of you're doing the latter, you just need one person to be comfortable with a megaphone, it doesn't need to be you. Disruption is mostly about physically blocking something, too, and less about the speech. It's okay to focus on speech, but that part of an event is more of a rally than a disruption. Organization is the real ticket, you will want to line up friendly media, be prepared with talking points, etc. Also consider starting small so you can get practice with lower stakes.