The earliest pseudo-hairjob I've seen on film is from Nympho Cycler (1971), directed by Ed Wood. The earliest proper hairjob is from a French film called Langue de Velours (1976), though it's using a wig. Actually, on that note, a short film called La Chevelure (1961) has a man stroking himself with a wig, though you don't see anything explicit. Still, that would have to be the first!