The key to your question isn't how long THC* metabolites can be detected but the incorporation rate (ICR) into hair. Infrequent use isn't incorporated into
hair. Rather occurs only after use on a regular basis across a period of time. So based on your description there would be no THC in any body hair. "Drug testing technology that detects the residual presence of cannabinoids and/or their metabolites in the hair typically fails to identify occasional marijuana users."

DuPont 2008, Random Student Drug Tests Are They Effective for Identifying Occasional Drug Users? p. 8

Galanter & Kleber, 2011 Psychotherapy for the Treatment of Substance Abuse, American Psychiatric Publishing, Wash, DC, p. 58


*meaning any cannabinoid including THC-COOH.