Cannabinoid Hyperemesis Syndrome (CHS): This condition is characterized by recurrent episodes of severe vomiting, often relieved by hot showers, and is associated with long-term cannabis use, which includes vaping products containing THC. The patient's daily vaping use and the specific relief from hot showers make this diagnosis highly plausible.

Gastroesophageal Reflux Disease (GERD): Although less likely given the specific relief from hot showers, GERD can cause abdominal pain and vomiting, especially if exacerbated by certain foods or positions.
Gastroparesis: This condition involves delayed stomach emptying, which can lead to nausea, vomiting, and abdominal pain. It might not fully explain the relief from hot showers but could be considered given the severity of symptoms.
Peptic Ulcer Disease: Ulcers in the stomach or duodenum can cause abdominal pain and vomiting, though the pattern of relief with hot showers is not typical.

Appendicitis: Although the symptoms do not classically present with vomiting relieved by hot showers, appendicitis can cause abdominal pain and vomiting. Missing this diagnosis could lead to severe consequences, including perforation.
Intestinal Obstruction: This is a surgical emergency that can present with abdominal pain and vomiting. The absence of relief with antiemetics and the severity of symptoms warrant consideration of this diagnosis.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause chronic abdominal pain, vomiting, and changes in bowel habits. While not immediately life-threatening, missing IBD could lead to significant morbidity.

Cyclic Vomiting Syndrome: A condition characterized by recurrent episodes of severe vomiting, often without an identifiable cause. It's less likely given the association with vaping, but it could be considered if other diagnoses are ruled out.
Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE): A rare genetic disorder that affects the digestive system and nervous system, causing severe vomiting among other symptoms. This would be an extremely rare cause and likely only considered after extensive evaluation and ruling out of more common conditions.