Triple-X /ˌtripəlˈeks/
adjectiveINFORMAL
adjective: X. X.X
relating to or denoting p. o.r. n.o. g.r. a.p. h.y of an explicit or extreme nature.
"p. o.r. n has moved out of the seedy bookshops and triple-X theaters"

What is implied in this sentence from mark twain's "the ? 1,000,000 bank-note"? i was puzzled, and wanted to discuss the matter a little further, but they didn't; so i took my leave, feeling hurt and insulted to be made the butt of what was apparently some kind of a practical joke, and yet obliged to put up with it, not being in circumstances to resent affronts from rich and strong folk.