Green’s Dictionary of Slang

(US) bad halitosis, or any bad smell.

[1928		E. Milton To Kiss the Crocodile 192: The rising screech and roar of half trafficking London borne on an upward gust of old dragon’s-breath!].
1977		Shryack, Butler & Slade Car [film script] Ugh – you’ve got dragon breath! [HDAS].
1984		Columbus et al. Gremlins [film script] You’ve got dragon breath. Bad breath [HDAS].
1992		R. Price Clockers 198: Y’all got to brush them teeth twice a day, my man [...] You got to fight the dragon.
2002		FW mag. 🌐 Preying on the Fear of Dragon Breath [...] Would you believe that in ancient times, bad breath was considered to be evil? And to solve this bad breath, it was recommended that people burn a small animal and rub its ashes on their gums.