that thing is all you can think about?
Like - whatever you do, don’t think about a PINK ELEPHANT!
Betcha can’t help it!
Well, DUH!!!
My brain just went ‘meh’. And proceded to not think about a pink elephant.
Pink elephants…don’t think…
YOU MADE ME LOSE THE GAME!!! Dammit, and I hadn’t lost for 9 months.
Doea thinking about what kind of shoes would a pink elephant wear count? I wasn’t think about teh elephant here, just the shoes 
A friend of mine in law school said she had a professor describe the use of exactly this as a ploy in a court case. Essentially the attorney tosses something out there that he/she shouldn’t. This generally gets a response from the judge to the effect that the jury should ignore what they just heard. Of course, now it has really been hammered home and they are thinking about it like crazy.
Of course this ploy can potentially get the attorney in trouble and/or cause a mistrial but used judiciously an attorney can probably get away with it.
The example the professor used to illustrate all this to his class was, “Do not think about a Pink Elephant!”
In my version pink elephant is replaced by your grandparents/parents having sex. On your bed. 
Margaret Thatcher in full bondage and discipline regalia was mine.
Augh! Damn it, I lost. Damn you!
Ha ha! I win, for I cleverly went over to thinking about a purple alligator!
which soon turned into a pink elephant engaged in some rather…interesting positions with the purple alligator.
dang.
Pay up.