Why is Mr. Jones in a foul mood and what does he do at the Red Lion?

In chapter 2, Orwell writes that Mr. Jones had recently fallen on hard times and had become disheartened after losing a significant amount of money in a lawsuit. Mr. Jones is deeply depressed and begins drinking heavily each day of the week. Instead of maintaining his farm and taking care of the animals, Mr. Jones spends the majority of his days reclining in his Windsor chair, reading the newspaper, and drinking alcohol. Mr. Jones's men were also dishonest and idle, which only made conditions on the farm worse for the animals. On the Saturday of Midsummer's Eve, Mr. Jones got so drunk at the Red Lion that he did not return home until midday on Sunday. Instead of feeding the animals and taking care of them when he returned to Manor Farm on Sunday, Mr. Jones went immediately to bed. The starving animals could not take being neglected and mistreated any longer and rebel against Mr. Jones. The animals successfully drive Mr. Jones off the farm and establish Animal Farm.

To answer this question, take a look at chapter 4. According to the narrator, Mr. Jones spends most of his time sitting in the taproom of the Red Lion pub, complaining of the "monstrous injustice" that he has suffered because those "good-for-nothing" animals evicted him from his own property. In other words, Mr. Jones is in a foul mood because his own animals have taken away his farm. He now spends his time drowning his sorrows in the nearby pub.
Initially, the other farmers offer Mr. Jones sympathy, but they do not offer him any help. However, they are very worried that a similar rebellion might occur on their own farms. This is particularly true of Mr. Frederick and Mr. Pilkington, who own farms adjacent to Mr. Jones and who are anxious to keep their animals in line.
With Frederick and Pilkington's help, Mr. Jones attempts to recapture his farm but is once again expelled from the property, leaving the animals in total control.