A person who acts and thinks highly of themself because they know how to significantly offend other people or do great damage towards other people when they get angry or want revenge, but when someone does the slightest thing to them, they cry and whine like a little bitch.

Another synonym is a glass gun. Comes from video gaming and role-playing games, when you have a character and/or weapons that have high offensive power, but weak defensive power.
Person 1: You know Katie and Chad are glass cannons, right?
Person 2: What do you mean?
Person 1: Because they hold a lot of clout and they love starting unnecessary conflict with people to slander other people and they can fight really well, like seriously they can beat your ass. But as soon as someone does one bad small thing to them, they fracture and shatter like a glass chalice.
Person 2: Oh yeah they're both weak bitches for real.
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A girl with great looks but little to no substance; a weak constitution. These girls are generally shallow and usually fall for the "bad boys," which are the boys that treat her like crap so she has to constantly qualify and validate herself.
Dude, don't go for Tomi. She's a glass cannon.
by pydrasparadox August 6, 2020
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Someone who has no issue criticizing others, often to an extreme extent, but gets extremely defensive when he is under criticism.
He’s a glass cannon critic, which is why we hate him.
by Salvguard January 12, 2020
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A moderation system in which it is effectively a glass cannon, usually consisting of slight discrepancies or bias to result in a mishap in servers.

This is most common in communities with corrupt moderation teams or outright bad ones.
Otis: "bro did you get banned from the forum"
Paul: "yeah, their Glass Cannon Moderation banned me for something slightly inappropriate when he wrote 3 troll posts"
by Not AstroSoup_ May 6, 2022
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tailow
damn thats a glass cannon
by twwhw February 6, 2022
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EVE Onlines bombers, like Nemesis.
Person 1: dude there’s a Nemesis on D-Scan.
Dude: don’t worry it’s a glass cannon, you should be able to blow it up
by VesperTheCoffeeAddict August 2, 2022
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