Lord Ye professed to love dragons

In ancient times there was a man called Ye Gong who was very fond of dragons. In his home everything, including the walls, windows, doors and even articles of daily use, were decorated with dragon designs. A real dragon was quite impressed when it heard about this, so it went to visit Ye Gong. However, when it stuck its head through the window Ye Gong was frightened and ran away. 

传说古代有个叶公，非常喜欢龙。他家里的墙上、柱子上、门窗上到处都画满了龙，连日常生活用的东西上也画着龙。天上的真龙知道了。非常感动，就下降到他住的地方，将头伸进窗户，尾巴拖在厅堂。叶公一见真龙。吓得脸都变了颜色，拔腿就跑。

This idiom satirizes those who profess to like or support something, but are averse to it in actual practice.

“叶公好龙”这个成语比喻表面上爱好某种事物，但实际上并不真正爱好。或者假装爱好，实际惧怕。