Yob is originally back-slang for boy, as is yennap for penny. In the phrase dab it up with (to sleep with) the dab was originally deb, backslang for bed. Of these, so far as I know, only yob remains in current usage.
For more backslang words, see here... http://people.sc.fsu.edu/~jburkardt/fun/wordplay/back_slang.html
In 1994, Tom Petty's censored radio version of "You Don't Know How It Feels" featured the word "joint" reversed to avoid overt drug references in the song. It sounded like "noij".
In 2003, Missy Elliot's song "Work It" also featured lyrics in reverse. Most listeners mistakenly thought that it was gibberish, or were unable to derive the meaning.