Find text to trigger a particular emoji in Predictive Keyboard
In English, the word you want is any of:


crazy
lol
laughing
lolz
lols
lulz
rotfl
rotflmao
excited
silly
loco


On macOS the list of words for the suggestion/predictive feature is in FindReplace.strings within /System/Library/PrivateFrameworks/CoreEmoji.framework, but the majority of the keywords work on iOS too.

There are different sets of words for each language, as you would expect.

Also see: How to bring up a precise Emoji in the iOS QuickType menu