Stingrays are very safe in that they aren't aggresive, you can bully the hell out of 'em but they'll just swim away.

Having said that I have NO intentions of touching a sting ray, ever.

There is an urban legend stating that daddy long-legs spiders have the most potent venom of any spider, but that their chelicera (fangs) are either too small or too weak to puncture human skin; the same legend is also repeated of the harvestman and crane fly, also called "daddy longlegs" in some locales. Indeed, pholcid spiders do have a short fang structure (called uncate). However, brown recluse spiders also have uncate fang structure, but are able to deliver medically significant bites. Either pholcid venom is not toxic to humans or there is a musculature difference between the two arachnids, with recluses, being hunting spiders, possessing stronger muscles for fang penetration.
Pholcid venom has never been scientifically tested on mammals. This would normally require milking the spiders and injecting the venom into humans or mice. In any case, there are no known cases of a pholcid spider ever biting a human and causing any serious effects.
In 2004, the Discovery Channel show MythBusters set out to test the daddy long-legs myth (season 1, episode 13 "Buried in Concrete"). After measuring the spider's fangs at approximately ¼ mm (average human skin thickness is about 0.10 mm) the show's host was apparently bitten, although the bite produced little more than a mild short-lived burning sensation. This appears to confirm the suspicion that pholcids can penetrate human skin, but that their venom is practically harmless to humans. Additionally, recent research has shown that pholcid venom is actually relatively weak in its effects on insects as well.