lethologica: the inability to come up with the right word. If you have lethologica, you'll never remember lethologica when it's the exact word you need.
If you're going to write your own vows for your wedding, make sure you write them down and give them to your best man or maid of honor. I wrote some great vows for my wedding, full of symbolism, imagery, and and poetry, and spent the week before the wedding memorizing them. When the wedding day came around, and it came time to say my vows, I remembered the first word, and then was struck by lethologica. A long pause ensued. I didn't have the future me there to make sure I had given the vows had written to my best man, so I was on my own. I eventually remembered the final parts of the vows and had to go with that. The abbreviated vows weren't nearly as awesome.
After the ceremony, people attributed the pause to my being overcome with emotion. Although that was technically true — if you consider stage fright, then embarrassment, then disbelief at my own inabilities emotions — it was really just a case of underpreparation and overconfidence.