because "piss on your chips" means

[username34939508]

something different to me than the way it is used here?

My definition:

To put yourself at a long-term disadvantage through a foolhardy short-term action.

Whereas on MN it seems to mean spoiling someone else's fun.

I do appreciate the fact that meaning is important to you, OP.

Have always thought it was someone who ruined another s not not an act of sec-sabotage as such

Ho

Oops self sabotage not sure where ho came from either!😅

Spoiling someone else's fun like "rain on your parade"
This has just reminded me of my favourite (deliberately) mixed metaphor, exbf's "Don't piss on my parade"

Yes, it's 'who pissed on your chips' ..... as in who spoilt your fun

You had something really good / really fun / really nice (ie your chips) and someone has come along and ruined it.

To put yourself at a long-term disadvantage through a foolhardy short-term action. is more 'Cutting of your nose to spite your face'