Next, add some obscure OC lore about fantasy world tree sap that acts as a powerful analgesic. It only works on dragons. It's very effective at treating otherwise-intractable pain, but is also powerfully addictive. Tahiru has repeatedly refused to use it even when clearly medically appropriate, fearing he lacks the strength of will to avoid addiction, and the consequences (to himself and others) if he succumbs. He's deadly serious about it, and has endured days of avoidable agony because of these concerns.
Thus, the humor lies in the depicted behavior being the polar opposite of "canon" lore.