Oh, yes, I can tell you that Mars in Gemini is truly the voice of hell. Well, not all the time, but when pushed to explain myself, I can do it and do it well. It's when I explain too much that I catch myself and realize that the person I'm speaking to is really sick of me talking.
I'm trying not to hate this placement. This is because I have Gemini rising, Sun AND Mercury in Gemini as well as Mars in Gem. It's absolutely ridiculous.
AND my Sun and Mars (in Gem) are conjunct my Asc (in Gem.) Also, my Sun is conjunct both Merc and Mars. Almost everything Gemini in my chart is conjunct.
I find if I focus on the Gemini in my chart, I realize I don't like it. I have to try SO hard not to over-talk or overanalyze things. I can verbally kick your @ss if you try to argue with me or debate something. The kicker is that I can do it EVEN IF I'M WRONG! I can state it to make it seem like I'm right (probably because I'm so good at getting to the bottom of an issue that I can pull through some nuances that actually ARE correct, then make them seem important to the issue, thus make it seem like I'm right.) God, it's terrible.
It helps me to be humble and let things go. It also helps me to remember that I am not just an air-ruled chart. I am extremely affected by the Moon and Neptune and am so empathic and compassionate that I almost cannot handle it. I have this watery influence that softens the air and makes me just as watery as airy.
I guess what I'm saying is that "on paper" my chart looks quite airy and Gemini-ruled. But going deeper to see the less obvious reveals the watery influence (and a good balance of fire and earth as well.)
My daughter is the opposite - her chart, by glancing at all the planets in the signs, is completely ruled by the Moon & Neptune, having 4 planets in Cancer and 2 in Pisces, with barely any air.
But going further, it turns out that she has just as much air as she does water. It boggles my mind (as I'm not a professional astrologer) how charts that look one way can be broken down by professional astrologers to reveal other influences.
Well, see? Gemini at it's best here. This reply can go on for days if I don't end it now.