I blow my nose at the table.
If it was a fancy restaurant with a low level of noise, I’d be quiet about it… but that’s less about the nose-blowing, and more because I’d try to be mindful of my noise level overall. At a café, with its relaxed atmosphere? I wouldn’t think twice.
I do know that some people consider it rude to blow their noses in public. I was with someone who’d been sniffing a lot, so I offered them a tissue which they politely declined, and then we got into an interesting discussion about just how different “proper etiquette” can be depending on someone’s background. Ultimately, though, they didn’t mind if I blew my nose, and from then on I didn’t offer them a tissue, neither of us cared, and that was the end of it.
I do think if we’re out in public we should expect to encounter behavior that’s different from what we’d do, or what we’d consider “proper.” We don’t live in a society where everyone follows the same etiquette book. And isn’t that half the fun?