Short-lived happiness
At the end of part 2, it seems that Paul has finally got his life on track, having found his future wife Margot. However, just after Paul makes a toast to his great fortune, he is ironically arrested and taken to jail.
Paul's expulsion
Paul is expelled from Oxford University after accidentally finding himself involved with a number of shenanigans in the Bollinger Club. However, he is arguably unfairly punished as he was simply in the wrong place at the wrong time.
Guardian
Although guardians are in a position of duty and care to whoever they are looking after, following Paul's expulsion he is denied access to money and accommodation from his guardian. As such, Paul's guardian is not fulfilling his duty as a guardian.
The sporting event
While teaching at the school in North Wales, Paul is asked to run the sporting events in the school. This is humorously ironic, as Paul is not an athletic or particularly active person, making this a struggle for him.