That's not what it's about, people

what about people who swear a bunch in their memes

From Merriam-Webster:

"NSFW - not safe for work; not suitable for work — used to warn someone that a website, email attachment, etc., is not suitable for viewing at most places of employment."

In other words, imagery that would get you into trouble if you were seen viewing it at work by your boss, or anyone else who might decide to become offended by it. Typically, this would be imagery containing sexual, violent, or some other content that would/could be deemed inappropriate in the workplace. As you might expect, this all started with the males of the species viewing images of the females of the species on their computers at work.

Notice that the Merriam-Webster definition does NOT apply to the email message itself.

That's because it's assumed that someone walking by your desk couldn't read every word of text on the screen of your laptop or other electronic device.

As for "bad words," people can and do become offended by seeing them on the internet every day. To a certain extent, this is understandable. Some people, especially younger people, aren't ready to see everything that's out there. And BTW, I'm not in favor of anyone intentionally offending anyone else; that would not be good manners, at least.

But applying "NSFW" to "bad words" is silly, and anyone who does this instantly demonstrates to everyone else that they don't understand what "NSFW" really means. "Bad words" could be restricted in given environments, say if young people were present or were users of a given website, with some tag like "that text is inappropriate for younger users."

For example, "Grendel" by John Gardner is a book that's often been banned simply for its text. The novel had no offensive imagery in it at all. A hypothetical first-grader might get in trouble if he/she/it carried it to school in they/them's bookbag, but trying to apply "NSFW" to that situation would be ludicrous.

As for imgflip, and as the site is commonly used, "NSFW" and "that text is inappropriate for younger users" have been mangled together as an expedient. But that's also silly.

Sorry for the long comment, but I wanted to answer your question fully and completely.

in tos its says exsesive swearing means that the meme must be nsfw (yes i did check tos)

imgflip.com/terms doesn't say that, or mention NSFW at all.

oh sorry i ment the second to last part of the page that comes up when your picking a stream to post in