This phrase is not really a slang term but rather an idiomatic expression. 'Móntate en un clavo caliente' is a colloquial phrase in Spanish that is generally used to tell someone to get into trouble or to get involved in a difficult or uncomfortable situation.
Examples
- Spanish: Si sigues faltando al trabajo sin motivo, pronto te vas a 'montar en un clavo caliente'.
- English: If you keep missing work without reason, soon you're going to 'get yourself into hot water'.