Obviously PAINT, especially something more on a primer concept than finish paint. The difference? Primers are formulated to bond with various surfaces and offer material that finish paint can then bind with. Something designed as a primer for glass would be the idea.
Of course, being so obvious, perhaps its builders thought about more variations on the theme than I will and worked out solutions for some of them without making the robot a paint fiend rather than a hero fiend.
Personally, freon sprays really would be easy and safe to carry, even for a hero's scheduled activities, and (BIG "and" here) assuming they really can hugely cool a mass of material as quickly as people said they could some years ago, complete with then shattering locks, etc. (bear in mind that lies and fakery existed long before YouTube "hack" videos and that I've never seen
IRL it done), a simple device for the hero to construct (Buy? How common are these robots and how many people need to defeat them?) would be a stick that could be made sturdily enough to serve as a nice "whacker" when needed or after usage, containing a spring-loaded or gas propelled shaped plug, probably of metal, picture those
car window when you are the first person in 20 years to drive off a bridge and begin to sink and can only escape if you have a special little hammer with a pointy end to break a window and swim free through the ensuing strong rush of water into the car hammers. Second feature on the end would be an opening positioning a nozzle along the same axis as the glass-breaker connected to a pressurized supply of freon, and away from the end, a sensor for the pressure of the freon, and a firing mechanism (which could also be on the end, to contact-fire the weapon, er... tool).
The idea would be to thrust the end of the "whacker" into the glass, triggering the freon which would spray just fast enough to hugely cool the glass surface (probably not very deep) without being sprayed so fast that most is just wasted, and when its pressure falls to a set value, firing the plug with the conical tip to focus the force on a very small area which would possibly break the whole glass component, but more probably you'd hope would break the outer layer enough to craze it to the point of messing up the incoming images to the point of unusability.
Or, you know, lower-tech, a simple hood, or 15 (they'd be easy to carry and one could keep applying them as the robot worked on removing them), that one applies over the sensor stalk. If it's a surface of the body plate kind of thing, think forklift fork, or rented Ryder truck in the 40 watt range, I mean, in the 22 foot-long range, filled with metal bought at a scrapyard for extra momentum to transfer. If one cannot bring large machinery into play, just a big sheet would raise your "hood game" to a new level.
Usually when something is designed a lot for certain problems, corners are cut elsewhere. A robot able to handle anything you do to its "eye" might yield to a sledgehammer applied elsewhere. Especially one that is more of a warhammer with a pointy, not blunt striking edge.
Flamethrowers are always a go to kind of tool. One isn't attacking a mountainside of pillboxes/bunkers filled with soldiers who literally want nothing more, in that moment, than to die for their emperor's glory (especially since they can see they are about to die anyway). So one needn't have a huge thing, just something that has perhaps two minutes of fuel available. Everything fears fire, even robots I bet! That's what makes those little trigger-fired, hand-sized soldering torches such wonderful self-defense tools. Seriously though, everything in existence is a pile of weak links holding together the good, no-compromises work. A minute or two of 2000 degree flame applied might not melt the outside of the robot or blind it, but it very likely would ruin enough of the weak links inside it to either stop it from working, or work at a much reduced effectiveness opening it to other tools brought along with the hero or ignored, OR open it to his electric-based attacks in ways not planned for by the manufacturer. And it could literally have sensors and routines that detect heat attacks and cause it to stop offensive action to make itself safe... to run from fire like a mugger/rapist in an alleyway. Because it's scared of fire.
But to again mention the warhammer idea, if a suitable one were to strike the robot's surface, especially if at the moment it sensed contact, a gas or spring fired bolt them amped up the damage by firing into the struck area, one might create enough of a hole, or even just insulation-damaged spot, for an electrical attack to enter the innards of the robot. It could be designed to be the channel for such for that matter: slam it into the surace wherever, the bolt fires amping the damage, and and electical connection from the bolt through the hammer to the hand wielding it lets the electrical attack the hero is powering reach righ through the hole or damaged surface to achieve the hero's goal. Without having to aim the attack at a possibly rather small spot of damage.
(Some of that doesn't address the bulletproof glass, mostly because it seems it wouldn't need to... so many ways to attack... so after folks get any enjoyment from the answer that they might find lurking in it, someone should consider deleting it.)