One of the bastions of urban legend tracking is
Snopes, where I often go to prove or disprove something.
Ones my mom has passed on to me, swearing they actually happened...
... the "waving" houseplant that was actually a giant spiders nest
... the tiny dog brought back from vacation that was really a large rat
... the gang initiation ritual of killing the first person to flash their lights at you
It's easy to lose half a day reading all the stuff at Snopes. Be sure to check out the lost legends section... those things are amazing!