Wearing the trousers is a reference to a man being in charge and when a woman wears the trousers she is the one in charge because trousers were traditionally worn by men who were traditionally the ones in charge
Masturbating, jerk off, choke the chicken, spank the monkey, beat the meat, whacking the pug, etc. etc.
Manually stimulating your penis with your hand to achieve orgasm.
Dave may be in the rugger club but I still reckon he's a south of the border trouser marauder by the way he shouts 'chase me chase me' when he's got the ball