Was spongebob squarepants supposed to be an adult show?

No, it just has some subtle jokes thrown in for the sake of parents who had to watch it with their kids. Most popular cartoons throw some hidden mature jokes in because kids force their parents to watch shows with them, and if the cartoon can keep the parents from tearing out their own hair in frustration they're more likely to put up with it which means better ratings.

No it was never pitched for an adult show. There havE been rumors about it and the creator evn said in an interview that it wasn't. The names just come from what the creature has or is. It was pitched to nickelodeon therefore they could never have anything like that on their network. If they were going to ptch it for an adult show like that they would show It on adult swim and adult swim said they never had a show like that pitched for them. Ur welcom

I think the writers wanted to avoid driving parents insane when they started and put in hidden "adult jokes." But then the homosexual spongebob and Patrick complaints started so the show was reduced to children only themed jokes.

No, it was always meant for kids.