Revealing mistake: When Tony goes to the bathroom and scans his blood toxicity, the Tony who faces the camera is supposed to be his reflection in the mirror, but the problem is the reflection is not reversed because it's not a mirror image, note Tony's clothing. Also, note how he scanned his right hand's finger, but then in the "mirror" he's sucking on his left hand's pricked finger. (00:28:30)
Revealing mistake: There are obvious differences in the appearance of the "Ironman" and "War Machine" suits throughout the movie, as pertains to them showing a digitally-rendered suit vs an actual physical suit that the actor/stuntmen wear. Whenever a real suit is shown on an actor, it is quite bulky, most noticeably around the abdomen/stomach areas, and the size of the head-piece.The digital versions are much slimmer in the abdomen areas and the headpieces are much smaller and more compact.
Revealing mistake: During the scene where the prism accelerator beam cuts through some objects, it is visible that the metal cabinet it goes through is pre-cut, and falls apart before the beam is even halfway through.
Revealing mistake: In the scene where the Senator is presenting the awards at the end of the movie, one of the microphones (third from the left) on the podium does not have a cable plugged in, which can also be seen in the next shot. In the proceeding close up shot, the mistake cannot be seen. In the very final shot before the credits roll, the same mistake can be seen. (01:56:10 - 01:57:00)
Answer: He wanted to do something nice for her, but since he is a pretty self-absorbed, shallow multi-billionaire, he forgot about her allergy. He remembered that there was SOMETHING about her and strawberries, but misremembered and thought it meant she really liked them. He makes a simple human mistake, not out of meanness or spite, but because he honestly does not remember.
Twotall