If you walk on eggshells, sooner or later they're gonna break.
It is a sign of a toxic relationship that you walk on eggshells worrying about your partner(s) reactions.
Put that baldly, it seems simple and obvious. Sadly, the slope between them can be awfully slippery.
Luckily, there's one clear difference between the two: whether or not people are owning their own emotions.
Here's an example that comes quickly to mind:
Both Goofus and Gallant have a celebrity crush on Chris Evans. Goofus denies having the celebrity crush because they're afraid that will make their partner mad or sad. Gallant is honest with his partner about having the crush, but doesn't mention it when their partner is having a rough day or feeling insecure.
See the difference there? Even though both might not tell their partner immediately, the difference is in how they're approaching it.
Goofus is taking responsibility for their partner's emotional state. They're fearing a negative emotional reaction of any kind, and so decides to hide how they feel.
Gallant is considering their partner's emotional state. Gallant knows the information may not be pleasant for their partner, so they try to tell their partner when they're able to receive that information. They remain honest about what they want and who they are, while still being kind to their partner.
Aside from the "hey, I want to have a healthy relationship" bit, there's a very practical reason why being honest about who you are and what you want and need is a good strategy.
It will come out anyway; you only get to choose how it comes out.
Walking on eggshells and hiding who you are and what you need - including things like irritations at behaviors or situations - takes willpower. And willpower (or mental energy) is as much a finite resource as the amount of physical energy you have.
This is why so many fights and arguments start in the evening and late night! Our mental energy reserves are low, so it's harder to balance on eggshells. And once our reserves are so low we can't keep it inside any longer, we have no energy to spare for consideration of our partner(s).
So rather than a difficult, but honest discussion, it turns into a nuclear meltdown.
It's possible to walk on eggshells around your partner for an extended period of time. It's born out of a fear that the difficult honest discussion will go badly. And sometimes they do; that's just the way things are. But I know people who walked on eggshells around their partner for years.
And sooner or later, that always - always - ends badly.