When BTC was around 100-200$, I remember someone sharing private keys at a certain time, and if you were fast enough you could transfer fractions of coins to your own key's address.  Actually I think that event was actually announced on Bitcointalk..

Out of fun I got over 0.1BTC at that time.  But some nice few thousand bucks today..


At that time, chain analysis tools to search for "tainted" coins from dark markets were still free to use. ...And of course, it turned out the free coins were all "tainted"