To encase, or otherwise stuff ones penis and scrotum, a.k.a. junk, into a very tight pair of leather pants. Smuffling is expanded to mean any rough tucking or handling, by oneself or others, of said junk, ranging from mild smuffling to extreme, drag queen smuffling (may or may not involve surgical staples).
Smuffling is also extremely useful when attempting to defecate upon your own chest.
"I tried to shit on my own chest, but my balls get in the way. I might have to do some smuffling to do it."