Ahhh, I think I got one:
Inside the card:
"Happy birthday Jimmy. I can't belive this little brat has lived enough to turn five. I got this card because I thought you would like it, it has those damn robots you liked so much when we went to see that f**ed-up film a few months ago. Gladly you are only five, and too f**ing dumb to read what's written here. Hopefully this will be the last birthday card I'll have to send you.
Screw you,
Grandpa
October - 1978
PS - Note to the parents: burn this card, I don't want the little f**er to read this when he learn to read."