Actually, antifreeze will taste fairly sweet (ethylene glycol). If it feels slippery, it's probably not windshield washer fluid (methanol/water). If it's salty, calcium chloride. If it's sweet, it's antifreeze.
Ethylene glycol is metabolized by alcohol dehydrogenase to form oxalic acid---and that's the stuff that is toxic. So, if you do decide to taste, rinse with water and spit. And then chase it with a couple shots of jack daniels---it'll fill up your ADH sites, and the ethylene glycol will be excreted unmetabolized.
Personally, I probably would go by "feel" and not by taste.