to-relax-in-the-gentleman's-way

to partake in "self pleasuring"

"wacking off"
"choking the chicken"
"knocking one out"

relaxing in the gentlemans way

Masturbating

"Roger decided to have a quiet night in in front of the television relaxing in the gentlemans way."

relaxing the gentleman's way

In a word- masturbating.

"Sorry, I can't come out tonight, I'm busy; I'm relaxing the gentleman's way."