Good question. It's not like she's the mother of somebody very important to the OP and therefore worth getting to know. Plus, he prolly just called his in-law outta the blue and was like "hey, let's go out to eat together." No way it was suggested by his girlfriend organically while they were all hanging out together. Wait.

I was being sarcastic. the wording makes the FML unclear

They might have been having dinner with their girlfriend and girlfriend's family, and the mom shot down the restaurant that OP suggested.

I think you need to look up the definition of sarcasm there, bud.

13, maybe you should. Not my fault it went over your head.

You wrote it, and the sarcasm doesn't come across at all. It's entirely your fault it went over everybody's head...

When you type, you have to make certain elaborations to make sure the sarcasm comes across. Typing a perfectly normal sentence and then claiming it to be sarcasm when everyone questions it doesn't work.

not my fault if you're not quick to catch on lol

OP asked his girlfriend's mother out to eat. OP's girlfriend's mother said that [restaurant OP suggested] sounded terrible. OP then saw on Facebook that OP's girlfriend's mother was tagged at [restaurant OP suggested].

I interpreted it as the mother actually likes the restaurant but only said it sounds terrible because OP suggested it, implying the mother dislikes OP which would be an FML to him.

Maybe he suggested it as a restaurant for a group that included her?

You did enough to click, read and comment.