My experience with Gemini (3 Flash) has been pretty funny, not awful (but worse than Kimi K2 or GPT 5.2 Mini), but it's just so much worse at (or rather hyper focused on) following my custom instructions, I keep getting responses like:

    The idiomatic "British" way of doing this ...

    Alternatively, for an Imperial-style approach, ...

    As a professional software engineer you really should ...

(Because I just have a short blurb about my educational background, career, and geography in there, which with every other model I've tried works great to ensure British spelling, UK information, metric units, and cut the cruft because I know how to mkdir etc.)

It's given me a good laugh a few times, but just about getting old now.