you can only get fat. If you got the rest of your diet and cardio in check you wont have a problem. But if your going to eat something like that then I'd say try to avoid eating it straight after a meal.
P.Z. It all depends on your goals. When I am contest dieting I usually reserve a cheat meal for every 4-6 weeks. I feel this helps with two things.......Sanity and keeps the body burning fat. Staying on diet for long periods can result in the body plateauing just like training. So every once oin a while you need to shock it. A cheat meal is one such way. if you are trying to just lose weight and lean out a bit an ice cream once a week is no problem!
Cheat meals are surely out during contest prep but otherwise, once a week
absolutely no harm. In fact (and don't ask me for the scientific explanation of this) the one cheat meal per week shocks the metabolism in such a fashion
that you burn more body fat over the long term than in fact if you did not eat the cheat meal.
Every Sunday evening my wife prepares my favorite cheat meal. Doing so
all the pent up urges during the week are satisfied and this has allowed me to maintian a clean diet for "years on end."