I've never been one to swear much. When I do, it's never around the kids, usually involves a hammer hitting my thumb, or sometimes when I've been hanging around people who do swear a lot, then it seems to slip out a little more often.
As for writing, while I love double-entendres, I don't use profanity much except in some dialogue. Two reasons for that. One, is probably just spending so many years in the journalism business you can't be dropping F bombs in your stories and expect it to get it past the editors (unless you're working now at some online pubs); and the other reason is my mom reads most of what I write and that pretty much keeps me on the straight and narrow.
But back to Seinfeld. Here's a good, in-depth story about him and what he's been up to lately: Jerry Seinfeld talks about how to be funny without sex and swearing
"Comedians are known for having long marriages," he says. Why? "I have to apologise for the self-serving answer I'm going to give you, but: we're smart. If you're smart, you stay married if you can. Marriage is hard for everyone – that's a basic fact – but it's a better life if you can do it. Very nice. Very relaxing. Very enjoyable."