Holy smokes you can - I put it down to the escalation of the GAS crisis to its final stages
FWIW I start with the middle finger on odd numbered days of the month, and index finger on even numbered days of the month - just for a little variety.....................................not really though - like A Douglas I haven't thought about this since at least 1979. A cursory glance over the last day or two suggests I vary this but goodness knows why - it's totally involuntary as far as I'm concerned but I think the index finger is the most usual
I actually have to think about this all the time. The are some faster (for me) riffs that I can only play without getting my fingers tangled by starting with my middle finger. I should add that my fingers are a bit weird. My middle finger is 3/4" longer (20mm) than my index finger. I have given up on trying to make them sound even and simply try too use the difference to my advantage. It helps make off beat accents come naturally
I do this on especially fast fills - I've just realised that if I play a repetitive fast rythmn, say continuous triplets (2 x 16th; 1 x 8th), I start with my ring finger, then middle then index. Or middle and index alternating.
While everybody has his or her own preferences I think that for really solid and consistent bass playing you should be aware which fingers are doing what when playing lines, runs, riffs etc. Otherwise you will never going to get it really tight.
And there should definately be a difference between doing a riff from low strings to high and the other way around.
Actually though, when I am playing country lines, playing root - fifth, I do often play the root with my middle finger, and the lower fifth with my index finger........when I am going up to play the fifth, I typically use the reverse fingering..... or I play both notes with my middle finger and alternate the fingering of any passing notes....
I jam with a guitar player who's missing all of his fingers on his picking hand except a little pinky nub. He uses it like a pick and jams amazingly well.
As for me, I don't think about it, but I bet I tend to lean on my middle more than the index or ring.
usually tap left foot, if at all. usually push the buttons on the pedal board with the right. And never chew gum at a gig. There, that should about cover all the bases.