When is it Okay to touch MAI?

The title may sound a little awkward, but it's important to understand that MAI don't hold many of the same stigmas that humans do when it comes to physical contact, and in some situations, maintaining said contact is a matter of safety.

When it's personally acceptable

Unlike humans, MAI don't have any place where it's really "bad" to touch them unless it's a particularly vulnerable area, like behind panels, in wheel wells, etc, but even then, that stems from a different place that's not nearly as bothersome, more of just a "you don't need to be poking around there," than anything. Of course it's weird to just put a hand on an MAI you've never met, because, of course, you've never met, but even MAI whom one is only acquainted with allow most all kinds of casual contact. (Ground/tank MAI don't have any nerves in their storage crates, so maybe this isn't the best place to sit with no contact to the main body of the unit...)

WHAT DID I JUST SAY

This isn't the case for every MAI you meet, but it's the general consensus that certain contact that may be considered personal by our standards is just fine with them as long as permission is asked for and granted. Need to get somewhere? Ask an MAI if you can hitch a ride either on or in them, and they'll probably be just fine with obliging. Casual contact can also be a part of everyday interaction and conversation. For example, a common greeting is to pat an MAI on their side or fender as it was a common gesture in the days of WWIII among units and their crews, and leaning on them is also pretty acceptable as long as you ask for permission first.

When it's for safety

Yes! There are actually times when it's dangerous to not maintain contact with an MAI regardless of acquaintance. They may

literally never do that, oh my god

have eyes facing in just about every direction, but they are eyes designed for distance; not close quarters. This means that just about every MAI you meet will have blind spots close to their body all around them. For example, all ground MAI are incapable of seeing their own wheels, rears, and lower glacis plates/lower fronts, most plane LAI have some degree of trouble looking at their own fuselages, and small to moderately sized planes cannot see the ground that isn't immediately under their landing gear all that well. This means that it is essential to at least keep one hand on an MAI when navigating a blind spot in the event that they move and don't realize that you're there.
The safest places to stay when interacting with an MAI in particularly close quarters is, for tanks and ground vehicles, anywhere in front of or beside their upper plates so long as you don't move behind the turret when it's forward-facing, or somewhere in the peripherals of the turret optics, and for planes, anywhere in the peripherals of their front/nose optics, or when moving under them, near their landing gear.