I had a teacher once who had a series of strange "coincidences" involving antifreeze and her pets. On Monday her dog "accidentally" drank a few cups of antifreeze and subsequently died. That wasn't so hard to believe in itself, but then the next day her cat and birds died from similar circumstances and then the next her fish somehow got a hold of the stuff. Though she thoroughly professed these to be accidents by the third day none, as is needless to say, were buying it.
Anyway. The active ingredient in antifreeze is ethylene glycol, which is a fatal toxin that will, if drank, metabolize into an oxalic acid and crystallize in your kidneys, eventually leading your eminent death if not treated. It's very sweet, which is why its common for household pets and young children to get ethylene glycol poisoning. It's also very potent, less than a teaspoon can down a midsized dog or cat before you even notice the symptoms.
To answer your question, yes, it's very bad for you.