I'm going back a good fifteen years or so here...
If anyone knows the Tolney Lane stretch of the Trent at Newark they will be familiar with Bob's Island and the point in the river that it comes to with the area known as the backwater to the far side.
I arrived on the gypsy site bank (Toney Lane) one morning around dawn to fish the stick and two blokes were fishing the point of the island opposite and had been there all night with keepnets out.
As soon as it was light enough out came the nets and with much clumsy handling fish, including some fair size barbel, were removed and photographed and to my utter amazement and further disgust, they were then placed back in the nets and chucked back out into the river.
Around lunchtime I could hear talk of going to the pub which was a short walk off the island and straight into town which they did whilst they left their gear on the bank with their cars parked behind and keepnets still out containing fish caught the previous night.
As soon as they were halfway up the island I reeled in and clipped up before marching off up the meadow further up my bank, crossing the narrow footbridge and down onto the island where I eventually reached their swim.
I pulled in the two nets, returned the fish and proceeded to cut off the entire bottom rings of their keepnets before throwing them back out again and quickly making my way back to my side of the river.
I hung around but they still hadn't returned over two hours later so I eventually left, I would have loved to have seen their faces when they next pulled them in ready for another round of clumsy handling and photographing one by one half to death.
So...
No, I haven't deliberately trashed my own gear but I have someone else's and without the slightest feeling of remorse