To tell lies, exaggerate; to mislead; to deceive.
I think you're bullshitting. Let’s just call your office and see if you even came in.
To have casual conversation with no real point; to shoot the breeze
I will probably just go and bullshit with Joe for awhile.
To come up with on the spot, to improvise poorly.
We just went on stage and bullshitted the whole concert because we didn't know any songs.