John is correct. I will add that "All I need" (or "That's all I need") is used so often in English that it is an established idiom. It implies that someone has been experiencing repeated difficulties in some area of life and is already highly frustrated. In the "Diary of a Wimpy Kid" books, Greg (the main character) faces many difficulties every day. A lot goes wrong for him. So when he says is "All I need is..." he is expressing his frustration, worrying that getting bullied would make things much worse for him. You may be interested in another idiom: "the last straw" (or "the straw that broke the camel's back"). This idiom means "the final event in a series of bad things that happen to make someone very upset, angry, etc." When someone says "All I need is..." in sarcasm or frustration, they feel that whatever they say next would be "the last straw" for them.

Hi John, The wimpy kid's statement is sarcastic. Sarcasm is where we say the opposite of what we really mean, and it is used when the real meaning is obvious to everyone. For example, if I am really worried and about an exam, I might say "I can't wait for the exam". The statement is sarcastic, with the real meaning being 'I am dreading the exam'. In your passage, of course the character doesn't want or need any bullies to target him. The fact that he doesn't want to be targeted is so obvious that he uses a sarcastic sentence to convey it. This sounds softer and a bit more light hearted than a direct statement. 'All I need' is a common phrase often used sarcastically to mean 'what I really don't need'. For example: 'All I need now is to get robbed' (The real meaning here is 'I really don't want to be robbed'). I hope that helps!