I just wanted to give you guys a few tips for getting this one without collecting the oysters.
To start with, when I got this achievement I had recently unlocked San Fierro. A few missions in, I was given a mission called Farewell my love, were you have to race against Catalina and her new boyfriend, Claude.
Upon completing this mission you are given a sports car (ZR 350), the car gives you an additional 50% sex appeal. I then drove it to the nearest safehouse and parked it in my garage, so it didn't dissapear and it was fully repaired.
It's worth noting you don't have to use that particular car. The cars which you can use are the Alpha, Banshee, Blade, Buffalo, Bullet, Cheetah, Comet, Elegy, Euros, Feltzer, Flash, Hermes, Huntley, Jester, Merit, Premier, Remington, Sentinel, Slamvan, Stretch, Sultan, Super GT, Tahoma, Uranus, Washington, Windsor and of course the ZR 350.
*Thanks to http://www.gtasanandreas.net/vehicles/
for that information*
Here is were the video comes in, I then did the sex appeal glitch shown in the video and built it up to 50%. To do this glitch you have to unequip your top by clicking the remove items tab, then torso and press a to confirm. You then go to Torso and select 'any' clothing item and equip it again, you then want to rinse and repeat until you are at 50%. To check this you simply press start and go over to the stats section. At the time I had a Rockstar Jacket which gave me an additional 3% each time, this may vary, not sure.
I then went to my garage, got back into my car and the achievement popped.
Bare in mind this is my first ever guide, be nice :p
*Thanks to Deranged Asylum for the updated video*