I get it by stamping down on every little bit of disrespect anyone ever shows me. If someone keeps displaying disrespectful behaviour towards me then they're out of my life. People can only treat you how you let them, so I don't let them.
With good people it's easy, they're automatically respectful, as I am to others, so the relationship flows easily. If someone feels like hard work it'll be because in some way or another they're a boundary busting bastard. The "hard work" feeling is you having to reinforce your boundaries all the time.
We tend to spend more time with a partner than a friend and we have greater expectations of a partner than a friend, in terms of support. So it's easier to hide incompatibility in a friendship (including in the level of respect you each show towards people) than with a romantic relationship.
It's possible to be friends with people with many different views, including those you disagree with, at least on a superficial basis. Most romantic relationships go beyond the superficial, which is where the cracks of incompatibility starts to show.
Someone naturally very selfish and disrespectful could pretend to be respectful, ie behave in an outwardly respectful manner regardless of their inner feelings, with their friends. This is because they don't have to keep it up for long. Then show a different side in their romantic relationships, if they're not naturally a respectful person, because nobody can keep up a pretense like that long term.
That's how you can get horrible, abusive (and by default, disrespectful) people where everyone who isn't their romantic partner thinks they're wonderful, because those people only see the "nice guy" act. If a friend is faking being a nice person, you'll never know unless one day their true feelings show through, which may never happen. With romantic relationships that day will definitely come, it's just a matter of when (and whether you recognise it for what it is, when it does happen). If you don't recognise it, you might stick around being disrespected and wondering why you feel somehow "bad" (upset or whatever).
It's worth remembering that a second chance isn't a "second" chance if it keeps happening! If someone treats you badly, then depending on the circumstances eg misunderstanding etc, you might want to give them a second chance. There's a reason why nobody refers to a "third chance" or "1000th chance", it's because these shouldn't exist! If someone treats you badly a second time it's probably the case that they're not someone who you should be around, for your own well-being.