What is the instrumental saxophone song in party scenes on SpongeBob SquarePants Such as when Spongebob has two parties meets strangler?

The instrumental saxophone song you're thinking of is likely "The Funky Stuff" by The Hightops. This upbeat and catchy tune is frequently used in party scenes on SpongeBob SquarePants, including the episode you mentioned where SpongeBob has two parties and meets the strangler.

It's a classic piece of SpongeBob music, perfectly capturing the fun and chaotic energy of the show's parties.