The couple was enjoying a night at the movies to watch a public screening of Iron Man 2 in L.A., but had chosen two seats already allocated to other cinema-goers.
The pair happily moved - but were forced to swap seats another three times as all their new spots were already booked, according to Britain's The Sun.
And to add to the Titanic star's embarrassment, the furore occurred during a trailer for his upcoming movie Inception.
A source tells the publication, "They were gracious and Leo was smiling at the irony of it. He clearly didn't realise you could reserve seats."