Man, I thought this was going to be a fun little thread about terrible gifts we've received. So much for that, but I'll throw my cap in the ring:
One of my exes got me the complete Hootie and the Blowfish discography on CDs about a decade ago. She was so proud of it and thought that I would love it, but not only a single disc was opened. When we'd have parties in college a friend and I who were familiar with popular 90s Hootie (Only Wanna Be With You, Hold My Hand, Let Her Cry) would sometimes drunkenly blast it and sing along. She apparently took that as a serious and sincere love for the 'fish and went all in on this Christmas gift.
I faked it, but I'm pretty sure she could tell. Felt bad, she hyped up what an awesome gift I was getting for weeks. We didn't talk much about it afterwards.