Alex Wain. (My comments are in italics.)
Age-otori (Japanese): To look worse after a haircut. (I could have definitely used this one a few thousand times.)
Arigata-meiwaku (Japanese): An act someone does for you that you didn't want to have them do and tried to avoid having them do, but they went ahead anyway, determined to do you a favor, and then things went wrong and caused you a lot of trouble, yet in the end social conventions required you to express gratitude. (I experience this a lot in parking lots, where people would rather be nice than just follow the law. You came to the intersection first; don't wave me on, GO!)
Backpfeifengesicht (German): A face badly in need of a fist. (Only the Germans...)
Bakku-shan (Japanese): A beautiful girl… as long as she’s being viewed from behind.
Desenrascanco (Portuguese): To disentangle yourself out of a bad situation. To "MacGyver" it.
Duende (Spanish): A climactic show of spirit in a performance or work of art, which might be fulfilled in flamenco dancing, or bull-fighting, etc. (Maestro Salazar used this word often.)
Forelsket (Norwegian): The euphoria you experience when you are first falling in love. (Why don't we have a word for this? We write enough songs about it!)
Gigil (Filipino): The urge to pinch or squeeze something that is unbearably cute. (In my lexicon, this is called "dental drills", because a friend once said to me, "They're such a cute couple, I just want to take dental drills to their eyeballs." It stuck, and now it's widely and casually used in my circle of friends.)
Guanxi (Mandarin): In traditional Chinese society you would build up good guanxi by giving gifts to people, taking them to dinner, or doing them a favor, but you can also use up your gianxi by asking for a favor to be repaid. (Meh. In-Laws.)
Ilunga (Tshiluba, Congo): A person who is ready to forgive any abuse for the first time, to tolerate it a second time, but never a third time. (Hey, that's my "3 strikes" philosophy. I'm ilunga!)
L’esprit de l’escalier (or l’esprit d’escalier)(French): Usually translated as "staircase wit,” is the act of thinking of a clever comeback when it is too late to deliver it.
Litost (Czech): A state of torment created by the sudden sight of one’s own misery.
Mamihlapinatapai (Yaghan): A look between two people that suggests an unspoken, shared desire.
Manja (Malay): To pamper. Describes gooey, childlike and coquettish behavior by women designed to elicit sympathy or pampering by men. “His girlfriend is a damn manja. Hearing her speak can cause diabetes.”
Meraki (Greek): Doing something with soul, creativity, or love. It’s when you put something of yourself into what you’re doing. (I really like this one.)
Nunchi (Korean): The subtle art of listening and gauging another’s mood. In Western culture, nunchi could be described as the concept of emotional intelligence. Knowing what to say or do, or what not to say or do, in a given situation. A socially clumsy person can be described as "nunchi eoptta", meaning “absent of nunchi”.
Pena ajena (Mexican Spanish): The embarrassment you feel watching someone else’s humiliation.
Pochemuchka (Russian): A person who asks a lot of questions. (Four year-old child)
Schadenfreude (German): Pleasure derived from someone else’s pain. (I know a couple of people who experience this. They also happen to be German.)
Sgiomlaireachd (Scottish Gaelic): When people interrupt you at mealtime.
Sgriob (Gaelic): The itchiness that overcomes the upper lip just before taking a sip of whisky.
Shlimazl (Yiddish): Somebody who has nothing but bad luck. (I've always loved Yiddish, and have always wanted to learn it.)
Stam (Hebrew): An agreement out of amusement and frustration that something doesn't have a satisfactory answer among those talking.
Taarradhin (Arabic): Implies a happy solution for everyone, or “I win. You win.” It’s a way of reconciling without anyone losing face. Arabic has no word for compromise, in the sense of reaching an arrangement via struggle and disagreement. (Well, that explains a lot!)
Tatemae and Honne (Japanese): What you pretend to believe and what you actually believe, respectively. (In English, I think this would be called hypocrisy.)
Tingo (Pascuense language of Easter Island): To borrow objects one by one from a neighbor’s house until there is nothing left.
Waldeinsamkeit (German): The feeling of being alone in the woods. (Is this literal, or figurative?)
Yoko meshi (Japanese): Literally, "a meal eaten sideways," referring to the peculiar stress induced by speaking a foreign language.
Thanks to Andrew McFall for the link!