開心果

Etymology
Said to be thus called from the shape resemblance to a smiling face. Alternatively, it may be a literal interpretation of, since most pistachio nuts dehisce, or pop open as they mature.

Noun

 * 1) pistachio nut
 * 2)  someone or something that makes people laugh, especially a lively and humorous person who keeps the group dynamic fun; barrel of laughs; life of the party