Our messy skits as I remember them, at least the ones that we could be arsed putting any planning into:
Disastermind - our first ever session was a "messy quiz for people who don't like messy quizzes" based around an old broken computer chair I had lying around. The rule were, you have a theatrical minute (ie as long as we feel like) to answer a series of questions. If you answer incorrectly, you will be gunged. If you pass, you will be gunged. If you answer correctly, but we feel like it anyway, you will be gunged.
The first round was a bunch of random questions dreamt up by Andy, the second round was a scripted skit, basically a bunch of puns to get me to "pass" as many as possible, using questions like "In football, what action describes the movement of the ball from one teammate to another?" (answer: pass) and "what fish, related to the trout, is fished for in both salt and freshwater?" (answer: bass). We ditched the second round after that, but the Disastermind format ran and ran, with more or less everyone getting a go in the black chair at some point. Andy still does it now, in his current projects.
Roget's Messaurus - As described above, our other 'gameshow' format for when we had more people to play with.
Wamdrogony Media Dating - We'd wanted to have a go at doing the most gungings possible in as many different outfits as we could. When I found an inflatable armchair shaped like a pair of giant lips in a car boot sale, we decided to do a video dating mockup. Messy Jo and I improvised a succession of bizarre characters getting gunged as we took turns recording our dodgy video dating ads as the other cleaned up and picked out a costume for the next one. In between we had Andy doing a series of morose pieces to camera, winging about all the horrible work we made him do. Aw, bless.
The lippy chair (as we christened it) developed a puncture halfway through the shoot, so the latter scenes were shot on a slowly deflating rubber chair. This somehow completed the concept, though it did nip any thoughts of doing a sequel in the bud.
GSCE sploshing studies - see above.
Satinic Rites - Our final messy shoot, and as Andy said, a piss funny one. With all of us dressed in satin of some kind (from posh frocks to pyjamas), I was the high priestess inducting a group of initiates into the "church of satin" via a bunch of daft oaths accompanied by a ritual gunging. This one got really out of hand towards the end, not least between Tits and myself.

Oh bloody hell, you've got me all nostalgic now.