Probably very thick natrasol as happened a few weeks ago.
Although there was a time in Scarborough were it went to the vote and I 'won' (or lost, depends on your perspective) a game called 'Custard Shorts' and getting it filled with the classic yellow stuff was pretty amazing. I wonder if anyone who was there remembers this???
In particular, when wearing a leotard or women's one-piece swimsuit as underwear. Pour the syrup in and then enjoy the feelings as it flows down and gathers in sensitive places, and the knowlege that it will, slowly, seep through the underwear and eventually also mess up the clothes you're wearing on top, but it will take a lot of time, and wonderful squelchy feelings, to do so.