MyDepressionList

I think it depends not on the emotions themselves, but on the overall resistance to mental suffering. Some people have a low threshold (whether it's adolescence or simply an innate "predisposition"), while others have a high threshold. The former are more prone to torment without any particular reason and all that. However, in general, you are right:

a "mental pain meter" (like a regular one) has not yet been invented. So all of this is speculation.