A father resents an ingrate son, forgetting that he too in his young days was an ingrate to a father now dead. Fate is not an unfair evenizer.

When a man blows his wad, at least two different things could have occurred: he either spent or lost all his money in a wager (his wad), or he spent or ejaculated his sperm (his wad). Thorne goes on to suggest that since at least the 1950s blow, in this context, is a euphemism for ejaculate.

I would guess it points up the difference between the involuntary chunder where you cannot choose the time place or direction, and the self-induced chunder which facilitates further consumption of alcohol after your theoretical limit is reached.

His paines, his pouertie, his ſharpe aſſayes, / Through which he paſt his miſerable dayes, / Offending none, and doing good to all, / Yet being maliſt both of great and ſmall.