Correct

兴头儿上

/ xìngtour shàng / 
Strokes

Example

As an Adverb

at the height of one's enthusiasm

1
Tā
他
zhèngzài
正在
xìng
兴
tour  
头儿
shàng
上
  
,
biè
别
dǎrǎo
打扰
tā
他
  
。

He is obviously enjoying himself immensely. Leave him alone.