I just got the whistle. Once you have both the lifeguard suit and the lifeguard buoy, walk around that tower nearest to the guy laying on the beach. I think I triggered it towards the back of the tower. One thing tho- it has to be equipped, not in costume but in the avatar tab. It happens that I did farm for both pieces myself but at this very moment, my friend is trying to trigger it using my lifeguard suit and buoy. I'll update when we figure out if it works for her or not. So far it hasn't.
I tried this with the items in the avatar tab, seems ill have to get the uniform T_T myself again...
EDIT: After trying, I conclude your character has to earn the items himself, trading his trash for them , then wearing just that in the avatar slots, and walking near the dead guy behind the watchtower , you willl get it.
Note: This items should be account bound, like the trash or sell only, this way the confusion that occurs trying to get the whistle whith someone else´s items wont occur !
Edited by xultrax, 03 June 2014 - 02:07 PM.