after once upon a december when demitri shows anya the tickets, what was the 4th one he throws for? who was he going to take?

It was either for the Circus, or the Royal Ballet I think... :P Haven't seen it for a while.

Well he said "well not that one"when he threw the 4th one.
Probably the royal ballet.

All four tickets were to the circus.

Well, the tickets were all for the russian circus. Dimitri would like to make Anya believe that there were only three tickets for Paris, but then he realized the fake tickets were four and so he thew one and said "not that one"