THOSE of a gentle disposition are strongly advised to stay well away from the vicinity of Jaffe Road tonight and also tomorrow - although, it has to be said, the meek as a rule stay well away from the Wan Chai district. The purpose for this Keeping Posted travel advisory is an alarming report which came our way that the high-spirited members of the territory's rugby and hockey clubs are planning to gatecrash the ''strictly by invitation only'' opening parties of Delaney's, supposedly Hong Kong's first Irish pub. We can't be sure that rugby boots and hockey sticks won't be used in any melee that might result on, er . . . Mother Kelly's doorstep if the rumoured social invasion takes place. But what we can say is that anyone with a genuine invitation will be able to taste the territory's first draught Guinness on tap. At least that's what hosts David and Sam claim.