What a lame joke hahahahaha. As Raquel has said: "El elemento químico que les recomiendo es el nitrato de meterla. La clase ha terminado". Nitrato = nitrate Ni trato de + infinitivo = I don't even try to... WARNING bad words from here on. In Spanish, when we are being informal/vulgar, we refer to the dick as "polla", "pija" or other regional variants. These words are usually feminine, so when we say "meterLA", that "la" refers to the dick. It would be something like stick it in. So, the teacer doesn't even try to get laid. We can see this -la in maaaaany other occasions. For example: "la tengo grande" would be something like "I'm hung" etc. Sorry if this you find this kind of speech offensive. I'm just trying to help. In any case, if you want to know more about this slang speech that books don't even mention, feel free to contact me :) Regards.

lo que dice este.... profesor es: "y el elemento químico que recomiendo es el NITRATO DE METERLA" jajaja la clase ha terminado. Es un mal chiste realmente, no me extraña que nadie le ria la gracia al...profesor. La supuesta gracia del chiste viene de separar la palabra NITRATO: Ni trato, que significa: ni siquiera trato (intento) de.... Realmente chiste malo y malsonante.