Yes, I have. Well.. kinda..
I really like potato salad (quite popular in Ireland). In the beginning of my undergrad, when I was still getting used to the college canteen, I saw potato salad on the menu one day. So I went for it, because it was all vegeterian (at least that's what I thought). I saw small little bits of what I thought was red onion... Couldn't really tell properly coz everything was covered in mayonnaise.
So I put the first spoon in my mouth and felt something chewy (potato salad is generally very soft and mushy in texture). And then it hit me... this is freakin ham!!!
I spit it out right there, didn't swallow it!! (Thank God there was no one else at the table with me). Drank loads and loads of water, put the salad in the bin, and recite astaghfaar.
And before anyone asks,... No, the menu doesn't specify the ingredients. Just the name of the dish and the price.
I've been very very careful after that and Alhumdulillah it hasn't happened to me ever again.