My pet hate is people lying to me or going behind my back, so when friends of mine distracted me (one pretended she needed a pencil case and dragged me to a stationary store), whilst they got a present for me, I felt really confused. On the one hand, I was delighted; I really appreciated the thought, but I also felt slightly duped I thought someone was actually asking for my opinion on pencil-cases and was heartily cooperating... I know that sounds ungrateful, but I really have a thing about honesty.
I don't think I would mind a present out of the blue, or a nice surprise, but not if it involves pulling the wool over my eyes (I'm the same with practical jokes).