I hate xmas, but birthdays are worse. Having a rehersed line is a good idea, "Thanks, this is awesome." or "O, now that is cool, thanx alot." and practice it, use different inflections. However I find the rehersed line doesn't work at family events and I really want to show my family that it does mean somthing to me that they care. In those cases I've found that if you just mention a trait of the gift or some way you can use it, "O, that frame will look good on my wall.", "These socks are soft.", "I like that color." or just ask a question about the gift, "Where did you get it?", "Is that all cotton?". You simply making the effort to take an interest in the gift will give them the sense that they are important to you and it shouldn't require to much extra.
I think of them like madlib conversations, "That is a nice X.", "Where did you find Y.", "O, I needed a C, where did you find it?" And practice, practice, practice. Say thankyou in a dozen different inflections, put together a list of positive adjectives that you can add to statements about things. What meaning people take from your words has as much to do with the words as it does with you demenor and body language and if you are confident the lines and actions you have rehersed for any given situations then others with sense that and natureally respond.
Good luck to all of use at this most stressful time of the year.
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For Evil to succeed, Good Men need only do nothing.