Why will they arrest you? Because that’s what cops are for: enforcing the laws of the government.

Why is operating a moving vehicle drunk against the law, even when it’s slow? Because even a skateboard can be dangerous to others when not operated with care. Since being drunk reduces your ability to operate anything with care, the more dangerous the moving vehicle, the more justification there is to regulate it under dwi/dui/owi type laws.

A riding mower is already an inherently dangerous machine, when operated sober and in the intended manner. Hundreds of pounds (and even more kilos) of weight, moving at a reasonable speed in your own yard can fuck shit up. Take it on the road where it isn’t supposed to be, get drunk, and now you’ve got the ability to kill someone else.

So, while cops poking their nose into shit and being tools of the state ain’t cool, if you’re out drunk and doing anything but walking, somebody should intervene. I don’t necessarily think that the default for something like a lawn mower should be a criminal offense on par with operating a car or motorcycle, but it definitely merits the person being secured away from said mower and cited with some kind of societal measures to reduce the chances of it happening again.

In other words, if you can’t act like a responsible adult, you get put in time out.