Shrine of the Storm - Shrine features a lot of trash pulls with high mob count which will obviously spawn a lot of orbs, but the boss fights are where this affix is the most dangerous. When Aqu’sirr splits into his smaller Aqualing forms, you will need to keep an eye on three different mobs that are spaced around the room. Council and Stormsong aren’t terrible, but then you’ll have to deal with Vol’zith. Vol’zith becomes incredibly frustrating on Explosive because each of his adds can spawn Explosives, and they will be spread out across the room. If you’re trying to keep the Whispers of Power debuff for the whole fight (as you should be), any one of the Explosive orbs going off will kill you, so Explosive makes this fight incredibly stressful.
The Underrot - Most of Underrot is actually not terribly affected by Explosive, but Unbound Abomination is a doozy. Each Rotting Spore on this fight can spawn an Explosive orb, and the Spores will be spread out all across the room since they spawn from the Vile Expulsion puddles. This fight already requires a fair bit of healing, so having orbs detonate (and you’re likely to have at least a few that do) will make the healer’s job a lot more difficult.
Temple of Sethraliss - Another dungeon where Explosive is only an occasional issue, but it can easily wipe you on some of the bosses. Aspix and Adderis will each spawn Explosive orbs, and this can be extremely dangerous because a lot of classes have incidental cleave abilities that will chain to the boss if you target the orb. If that boss happens to be the boss with Lightning Shield, you’ll get zapped. Adderis also melees players near him while Aspix is active, so any melee trying to kill orbs near him might get whacked. Avatar is the real headache in here, though, as each add on the fight can spawn orbs, and the adds are always spread out around the room. But the real kicker is that the toads ALSO spawn orbs, so when those start raining from the sky you’d better kill them as quickly as possible.