1. The act of 'squiddlepissing' is when suffering from diarrhea you sit down to piss and you let go and shit and piss large amounts simultaneously. You just squiddlepissed. The physics of the matter result in loss of accuracy and the resultant splatters are sure tell tale signs of a squiddlepisser.
2. The beige soup (mix of water, faeces, urine and possibly vomit) left in the toilet bowl afterwards can also be referred to as squiddlepiss itself.
3. Squiddlepiss can also be used in the same way as 'clusterfuck' or 'pigs ear'. To mean a mess that got out of control.
"Good job I sat down on the toilet just then dave, I squiddlepissed right up the back wall"
"Arrrrrrgh there's shit and piss on the underside of this window sill, someones squiddlepissed around here"
"So after I slept with her, i did her sister and then her mum, it was becoming a right squiddlepiss so I became gay"
"Oh dear, what did you do to my nicely organised toolbox? You've made a right squiddlepiss here"