Tough question. Is it the food? Overall experience? Level of fun?
I once shared bad food with someone I was in the process of falling wildly in love with (mutually). It was certainly memorable but not for the food.
I do remember a friend going fishing and we ate salmon just caught, so good. And some really good Thanksgiving dinners - one reason I like Thanksgiving is that turkey, sweet potatoes, cranberries and pies are all among my favorite things. Also remember the first time I ate various things (had quail for the first time on my sabbatical, also duck liver flan which sounds disgusting but was really good).
I simply cannot say what was my best food meal ever. But on my recent sabbatical I went to 28 different restaurants (not counting things like a cup of tea from Starbucks on I-5) and my best meal was at the Slanted Door in the San Francisco Ferry Building. It's billed as Vietnamese/Asian fusion. I started with duck confit salad. I'm very fond of duck and rarely cook it since it's such a pain in the butt to fix. Duck was perfect, very fresh greens, good dressing, really enough for two but I ate it all. Then I had (after much deliberation) pork noodles (clearly don't keep kosher!). A bed of rice noodles, a bed of very fresh and crisp bean sprouts and pork three ways; loin braised in a soy-sauce base, fried pork belly, very crisp, and minced in spring rolls, also came with some greens and dipping sauce. Everything was perfectly cooked and all the flavors went well together. They even had a special blend of tea. (next time I go there I'm trying one of their special cocktails). Dessert was entirely Western, two freshly baked snickerdoodles made an ice cream sandwich with super premium vanilla ice cream. The cookies were still warm from the oven so the ice cream was just beginning to melt around the edges. It took a few napkins to eat that. In my 28 restaurant California tour I learned that too many places don't do dessert well, including high end places, this one was really simple and so good.