Nop, no limit! If you know you are going out, just set a relistic amount of syns that you can stick to! Follow the plan upto that day as normal, have your daily syns and healthy Xs, use your flexi syns, then back to the plan straight away the next day!
I suppose, people that don't have a problem with their weight have "days off" but continue to eat "normally" around that day! I think that's how it works.