The most desirable form of cooked noodles. Just firm, not soft.
Also:
A wang that's not hard, but not soft; just a bit firm.
Adam: Trevor do you like al dente?
Trevor: No!
Jon: Haha Trevor likes al dente!
Adam: Hahaha he so does.
Trevor: Al dente is revolting!
Adam/Jon: Trevor loves al dente!
Undercooked pasta which, upon regurgitation, resembles a squirming mass of worms and maggots. Al dente literally means "to the teeth", as it is almost crunchy, meaning it is cheap, dried pasta rather than fresh, soft pasta.
For example a hastily-cooked friday night spaghetti before going out on the piss can be complimented as "al dente", however once one is blowing chunks in the form of long, strandy, red worms covered in stomach bile that tickle ever inch of your oesophagus, not to mention the back of your nose, down a back alley, soon becomes "undercooked".