Stop moaning and get out in the countryside for some real gunge to ride on.
There's slightly diluted cow pat. Slippery when wet, but dries hard enough to stop your gears working, and then try getting it off your clothes.
Assorted muds. Clay based ones are generally the slipperyest. Can of course be mixed with cow pat, different proportions give different effects.
Then there are squashed apples, to be found in cider making counties up the west side of England, Sussex and Kent, Brittany and Normandy, generally similar properties to squashed conker but stickier when it gets onto anything. Added benefit is its attractiveness to wasps.
A spill of slurry can be great fun. Guaranteed off if it's on a bend, and the stink once it's on you lasts for days!
Red diesel spilt on the road is just as good as the normal stuff you get spilt in towns and cities and in the eastern counties a few sugar beets squashed and mixed with rain water are always good for an off!
The real jewel in the crown is hedge trimmings. Most hedges just leave shards of wood which lie flat and only go through a tyre very occasionally, but of course there's always the hawthorn hedge to make up for that. What you really don't want to meet is a piece about the length of a tyre circumference with 20mm thorns sticking out in all directions at 5mm intervals. A few of those hidden under a selection of the surface coatings above is guaranteed to make any cyclists day - not.
And then there's foamy squashed conkers
