This will vary somewhat by jurisdiction. But in most US states:
- Bob happily blabs to the media and exposes all the other jurors and what they've said and who they are. All for some clout, or money.
If the authorities can trace these stories back to Bob (and they will put some effort into tracing them) Bob may well be found guilty of criminal contempt of court, fined, and sentenced to a short period in jail. He may also lose the right to be on a jury in future.
- Bob secretly tells the prosecution/defense that he'll do whatever they ask to manipulate the jury, for a favour.
If this comes out, Bob could be convicted of soliciting a bribe, and if the scheme went forward, of both accepting a bribe, and jury tampering (or either, depending on the evidence). These are serious crimes, and Bob might well spend several years in prison.
- Bob is a nutcase, and acts in bad faith to manipulate the jury just for the hell of it. For example, "filibustering" and wasting everyone's time, without explicitly stepping into maliciousness.
It is not unlawful to be a nutcase. The judge could order Bob removed from the jury if his disruptions were serious enough. If Bob actually violated th explicit instructions issued by the judge, he might be convicted of contempt, as in case 1, but this is rather less likely.
A comment adds the scenario:
- Bob knows that the guilt has been proven beyond a reasonable doubt, but still tries to sway the jury for a not-guilty verdict (whether he tells other jurors what's going on or not) and will hang the jury if that fails, because he doesn't believe the defendant should get in trouble for it
This is an instance of "jury nullification". Bob is within his legal rights, and cannot be punished, nor removed from the jury. Bob can try to convince the other jurors that the law is unjust, or that the possible penalties are too severe for what the accused did, or of some other reason not to convict. If they agree, and acquit the accused, the acquittal stands, however contrary to the letter of the law. If they do not agree, there is a mistrial because of a hung jury. The prosecution may (but need not) retry the accused.