Appendicitis: This is the most common cause of right lower quadrant abdominal pain in young adults. The pain often starts near the navel and then moves to the right lower quadrant. Appendicitis is an emergency that requires prompt surgical intervention.

Gastroenteritis: Inflammation of the stomach and intestines, usually due to a viral or bacterial infection, can cause abdominal pain, nausea, vomiting, and diarrhea. The pain can be localized to the right lower quadrant.
Intestinal Obstruction: A blockage in the small or large intestine can cause severe abdominal pain, nausea, vomiting, and constipation. The pain can be localized to the right lower quadrant if the obstruction is in the ileum or cecum.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause chronic abdominal pain, diarrhea, and weight loss. The pain can be localized to the right lower quadrant if the disease affects the terminal ileum or cecum.
Ovarian Torsion (less likely in males but can occur in cases of testicular torsion or other testicular issues): While less common in males, testicular torsion can cause severe pain in the lower abdomen, which might be referred to the right lower quadrant.

Ectopic Pregnancy (in cases of intersex individuals or those with a female reproductive system): Although extremely rare in a genetically male individual, it's crucial to consider in individuals with a female reproductive system or those with a disorder of sex development. Ectopic pregnancy is a life-threatening condition that requires immediate medical attention.
Ruptured Viseral Aneurysm: A rupture of an aneurysm in the visceral arteries can cause severe abdominal pain, hypotension, and shock. This is a rare but life-threatening condition.
Diverticulitis: Inflammation of a diverticulum in the colon can cause severe abdominal pain, usually in the left lower quadrant, but can occasionally be in the right lower quadrant if the diverticulum is in the cecum or ascending colon.
Mesenteric Ischemia: A reduction in blood flow to the intestines can cause severe abdominal pain, nausea, vomiting, and bloody stools. This condition requires prompt diagnosis and treatment to prevent intestinal infarction.

Meckel's Diverticulum: A congenital anomaly of the small intestine can cause abdominal pain, nausea, vomiting, and gastrointestinal bleeding if it becomes inflamed or obstructed.
Right Lower Quadrant Hematoma: A collection of blood in the right lower quadrant can cause abdominal pain and is often due to trauma or a bleeding disorder.
Carcinoid Tumor: A rare tumor of the neuroendocrine system can cause abdominal pain, flushing, diarrhea, and wheezing. These tumors are often found in the small intestine and can cause right lower quadrant pain if they are located in the ileum.
Intussusception: A condition where a part of the intestine telescopes into another part can cause severe abdominal pain, vomiting, and bloody stools. This condition is more common in children but can occur in adults.