Litter tray etiquette states that

[Wibblechick]

Another good one (Chloe favourite) is to show no sign of interest when the tray is being sorted, then the minute all is clean and tidy, discover you are BURSTING! 

So full, in fact, that you cant be bothered to sit down properly ..... 

So the resulting puddle manages to go over the edge of the tray .... 

And then Mr T arrives and while you are re-emptying the tray and wiping the floor, does a mega poo in the empty tray and tries to bury it wtih nothing ....

[Feline Costumier]

Dave likes to get in the tray while I'm scooping and take usually a poo and then scatter litter everywhere, sometimes he just digs around ,aking a mess to get in the way and be naughty 

[puddypaws]

Glad it isn't just me who has this problem.  Another good one is to perform right in the corner of the tray and then cover it and scatter litter all over the edge and cover the floor.  Little darlings   

[Mark]

A freshly scrubbed tray with a complete change of litter requires that the first user will have the squits in it 

Alice not only did that but flew out of the tray depositing clumps of pooey litter all over the surrounding floor. Luckily it is wood 

I find the Parazone toilet wipes priceless for things like that (1/2 price in Wilkinsons ATM)