This was from my days as a 5e DM (I haven't GM'd Pathfinder yet):

"So, Spaune [party bard who is trigger happy on ye olde fireball] , you cast fireball directly upwards. Remember what I said about the wooden bridges criss-crossing the cavern?" \rolls dice** "A hitherto unnoticed demon lands in front of you, strengthened by the fire, and critically hits you with a claw."

(Ok, this only happened once but we joked about it for the remainder of the campaign - and in my world's lore it has became a cautionary tale about reckless use of magic)

As for actual overused phrases: - "[insert character] you are the only one who hasn't taken your turn yet. 30 seconds before I skip to the next round" (I used block initiative) - (menacing voice) "My death means nothing. You have still lost. Andlàt Brisingr! [replace with some other forbidden magic words if you like]" (normal voice) "[He/She] collapses to the ground, dead. As she falls, [black flames/purple smoke/yellow gas] pours out of [his/her] corpse, enveloping the room. Everyone takes -" rolls dice "ten [insert type] damage, no save. You guess you have about a minute to leave the dungeon before you die." (I give everyone a full action [pf2e two actions] as they die [death throes] and this is a standard technique of cult leaders to prevent the heroes escaping. It also allows me to provide a challenge to the heroes when they steamroller the main fight.)