WHAT is a Secretaries' Jamboree? Do they sit around a campfire singing jolly songs and laughing like drains over Dumbest Boss of the Year stories? No, they climb into their glad rags, tuck into a splendid dinner, then settle back to watch a slick fashion show. Tropical Nights was the theme for the 8th Secretaries' Jamboree held in style this week at the Golden Mile Holiday Inn's Crystal Ballroom and attended by 250 of the best. As usual the annual ritual was unashamedly elitist: only top executive secretaries from Lufthansa's corporate accounts and accredited travel agents. Co-sponsor Triumph International laid on the works: its Summer '93 collection, presented in its entirety for the first time this season. ''Until tonight, we've only shown sections of it in Hongkong. This is the only event where we present the full range,'' said a Triumph executive as the super secretaries saw their favourite fantasies realised on stage. What a glut. Leisurewear, sportswear, swimwear, nightwear and of course, lingerie. Ironically, the foundation garments which used to be synonymous with Triumph were the least appealing. Also the least flattering, as even those svelte, lycra-encased bodies on the catwalk demonstrated. There wasn't the hint of a bulge to be seen with the rest. Some really smashing outfits for fun-filled days and balmy nights at some tropical paradise far, far away from that bossy voice saying: ''Can you take a letter?''