Green’s Dictionary of Slang

hee-haw n.

[the trad. transliteration of the donkey’s bray]

1. [mid-19C+] a donkey.

2. [late 19C+] (US, also hee-ho) loud, offensive laughter, esp. if scornful.

3. [20C+] derision, nonsense.

4. [2010s] in pl. the testicles.