Aside from the yellow sponge with his own television show, Spongebob also refers to any person invited or uninvited to a gathering in which that person does not provide any food items (e.g. spinach dip, chicken wings) or beverages (e.g. a liter of soda or a case of beer) and eats and drinks to his/her heart's content. Thus acting like a sponge.
Timmy: Hey Dave, nice party. I brought some coca-cola and Doritos for everyone to enjoy.
Dave: Oh! Thanks a lot Timmy. I'll set these right on the table.
John: Hey Dave, swell get-together. Where's the cooler? I'm parched.
Dave: It's right next to the porch spongebob.
Jake: I thought I asked you to bring over an extra case of Bud Light Lime Thomas!
Tom: Oh yeah, I forgot. Sorrry.
Jake: GET OUT OF MY HOUSE SPONGEBOB!
Robbie: That's his third beer in the last half hour. Who invited spongebob??