Green’s Dictionary of Slang

(Aus.) of a man, to ogle, to leer.

1999		G. Seal Lingo 90: uncle merv means to perv (as in ogle) and can be simply rendered as have an uncle.
2003		www.thepantsman.com 🌐 I was content to remain seated at the bar [...] doing the Uncle Merv on the magnificent talent surrounding us.