Let's go through some possible outcomes.
Aries Mercury can be a person who answers promptly. And they speak freely, they do not hold back, whatever they think, they can openly say. So other people can be shocked or disturbed by how easily Aries Mercury takes up space & shares their opinions.
They can also be argumentative, strong, principled, very sure in what they say. Challenge you on things. They don't mind getting into it verbally. They have the energy for that. And they are the first to bring attention to something, to call someone out, to be very upfront in situations where discretion is preferred.
They are also rather friendly, open, will start a conversation with you first, not shy. Warm. Sometimes hot.
They might speak quickly, or send many messages instead of just one large message, and be very forward.
Some of them can be very persistent, they don't leave you alone, they send threats, they blow up your phone.
They might frequently ask you to do things with them… go to the gym, go for a drive, a bike ride, play outside.
They could have grown up in loud environments. Their parents could have been loud, or their household can be noisy, or they can be in very active company. They might be used to someone speaking to them in a demanding, expectant, loud tone. They can witness violence. They can find themselves arguing with other people frequently.
They're interested in movement, they want things to change, to begin, for an awakening to happen. The way they speak can be motivational, or leader-like, or strong and intense, their delivery can feel very genuine and therefore funny. People either love them or hate them because Aries Mercury is highly energetic, individualistic in how they express, and they usually don't care if it bothers you, or they do care but they can't help how they come across.
They can be competitive and challenge you, or trash talk well. And think of the perfect answers right in the moment. They are definitely hands-on learners, and can ignore instructions, uninterested in reading anything before figuring it out. They can be into cars, engines, power tools, building stuff… or super into sports…
They can express in very childish ways and get along well with children. And they're likely to be into fun. Like yes, let's go to a concert, let's go to the bar, let's go horseback riding, let's go for a hike.
But they can also work in very high-stress environments where there is a constant sense of urgency, tension, movement, action. Like being a surgeon or a hospital nurse. Or working in a hot, busy kitchen. Or working with criminals or in dangerous, unpredictable environments. Mercury in Aries are also likely to keep animals, especially ones that are more aggressive or noisy, like loud birds or yappy dogs.
They're also very likely to be gamers. Particularly shooting or action games, horror games, anything that gets your pulse running.
Aries Mercury can be musicians as well, particularly drummers or trumpeters or electric guitarists, once again, instruments that have high energy.
— Just remember that your Mercury in Aries is aspecting other planets. This is important, because it adds important layers of detail. You can start by thinking of your Mercury in isolation. But try to then expand your understanding by connecting Mercury to other planets he aspects.