Context

This is a misquoted line from the play Hamlet, written by William Shakespeare (1605).

William Shakespeare is probably the greatest playwright of all time and Hamlet is probably his greatest play. That's why it might be kind of important to get all the words in the correct order when you're quoting it. Sorry. We're sticklers for the Bard like that.

And this one is so close. You'll usually hear it misquoted as, "Methinks the lady doth protest too much." But Queen Gertrude's line is actually, "The lady doth protest too much, methinks." The first one does roll of the tongue a bit more, we have to admit, but only because you've heard it said incorrectly so many darn times. Just move that first word to the caboose and you're good to go.

See, now you're quoting Elizabethan English with ease and accuracy. Go you!

Where you've heard it

You may have heard this in any place protesting ladies and misquoting humans could be found together. That's to say—anywhere on Earth. Probably one of the most widely known and misquoted Shakespearian lines of all time.

Additional Notable References: 

Alanis Morissette sings a whole song called "Doth I Protest Too Much" but she cleverly avoided the whole "methinks" thing and went for a different misquote of her own.

Pretentious Factor

If you were to drop this quote at a dinner party, would you get an in-unison "awww" or would everyone roll their eyes and never invite you back? Here it is, on a scale of 1-10.

The fact that this is Shakespeare bumps up your pretentiousness factor by about 30%. Then you've got the fact that you're misquoting the Bard on top of that. Just hope there's not an English major in the room when you bust out this little gem.