A fake or immaginary disease, usually to get out of work or for attention. Calling out someone who you know is faking it.
Mark: My tummy doesn't feel good and my head is hot. I think I am sick, I can't go to work today.
Tom:Bullshitinosis
Travis: Yes, Mark you have bullshitinosis, and IDS
Person 1: "Yo, I forgot about that project, I'mma just be bullshitting it tonight."
Person 2: "No way, it's worth too much of our grade. I've been fullshitting it for weeks."