Third-generation blunts can be made from the roaches of many second-generation blunts, fourth-gen from third-gen and so on, by which time you'd better be prepared to cough your lungs right out of your chest.
"For reals? We haven't smoked one of those since two 4/20s ago!"
"What generation was that blunt man? That shit got me so high!"
"Oh that? Man we quit counting after the fifth gen, we're just calling that one Generation X."