To be encouraged by someone who is not at immediate risk and/or safe from repercussions to do something stupid. Especially when subsequently caught or hurt.
Similar to peer pressure except that the snapper'er is unaware/ignorant of the actual risks.
Jim broke his leg after Tony told him it was safe to jump from the roof. Tony saw it on TV so he thought it was safe. Tony really snappered Jim good.
"Steve, stop telling me to steal the video game. I know for a fact they have security cameras. You aren't going to snapper me!"