In 2013, Actor 1 wore a piece of apparel on a TV show he hosts to promote Film 1 featuring Actor 2. In 2014, based on whatever had been revealed of an upcoming 2014 film featuring Actor 2, Actor 2 dared Actor 1 to wear a similar 'outfit' on the same TV show.
In Film 2, Actor 2's character is rumoured to play something or someone trying to be human. So identify the people involved in this sneak peek.
[+ Show Answer]
Actor 1 is Salman Khan, who wore a bowler hat to promote the film "Dhoom 3" for 'friend' Aamir Khan (Actor 2). Aamir Khan's "P.K." (some rumours say he plays an alien) released a poster featuring him in the bare essentials.
More here.