60% this. I wouldn't resign the game, but I'd make a mental note of annoyance and take special pleasure in calling out the other guy's rules mistakes and try extra hard to win. Shrug.
I get that this is a case where I'm not playing it strictly by the rulebook, and nobody can expect sympathy when they do that. But just to explain the reasoning, in this particular case I think people have slipped into this "bad habit" because it seems to fit the flow of the game better. I think that ending a vehicle's MPh in Bypass with MPs left to spare is so common that people just let it go and assume those excess MPs are spent in Delay or in having done the VBM by expending more MPs than necessary. That "feels more right" than whatever is indicated "by the book". You move in via Bypass, you announce you're done moving, bingo. Sure, your opponent may say "OK, but that was your last 7 MPs you spent there, so I'm gonna get 7 First Fire shots at you, and he's right, but that still "feels more right" than whatever the (correct, by-the-book!) alternative is.
Yep, I recognize that this logic is indefensible. I still would rather play it that way.
Could someone point out the game mechanic that's gained by playing it correctly? Maybe that's part of why so many people play it "lazy" - they don't see the value of what they're missing. If I have 7 MP left and I want to end up in Motion Bypass of a building that's 2 hexes away, what's better about the correct way (moving into the first hex at 5 MP, say [or moving in at 1MP and delaying for another 4], and then Bypassing the building for MPs 6 and 7) then the incorrect, lazy, way (moving into the first hex at 1 MP, then bypassing the building for MPs 2 and 3, then saying "I'm done" and acknowledging that the vehicle is also spending MPs 4-7 in Motion where he is)?
I mean, aside from "playing the game according to the rules", which is of course what we all should do, but if people don't understand why the rules dictate certain things, they're likely to play it lazy and wrong. That's all I'm saying.
There's so many ways to burn MPs (entering a hex at more MP than necessary, using Delay MPs) that it seems ... against the flow of the rules? ... to worry about how those last MPs are spent. I think that's part of it as well.
[Edit - reading this again, yeah, it's pretty weak. I shoulda learned it the right way a long time ago and just gotten into the habit of doing things correctly. Funny how one can get so attached to one's own biases and quasi House Rules. I still would rather play it the lazy way, but I don't think I'll be so annoyed if my opponent expresses a desire to play it correctly. Look, even after playing this game forever, sometimes you gotta accept that You've Been Playing It Wrong.]