A shield of fire comes down by your greatest enemy, making them invulnerable.

I cast Tasha's Caustic Brew

You cast it but the DM, not having access to it, rules that it fails. 

I cast Thaumaturgy to open a door.

The door opens and once opened cannot be closed. Through the door is something you did not want to see between your mother and the rogue. She's helping the rogue full of tax forms! The image is broken forever! 

I cast Clone. 

A rogue paying taxes instead of committing tax fraud? How scandalous!

Unbeknownst to you, the clone has an inhibitor chip placed within it that causes your character to have a sudden and uncontrollable urge to hunt down jedi, even if there aren't any jedi in the setting.

I cast Unseen Servant

The servant drops a heavy suitcase on your foot

I cast Detect Evil and Good

Your DM is Obi-Wan and you detect Evil... from a certain point of view. 

I cast Bless

you bless your enemies and they attack you

I cast Invisibility

Not realizing you're around, your fellow party-members decide to do things like picking their toes, belching loudly, and little happy-dances that they'd never do around you. 

I cast [spell[Create Bonfire[/spell]

You burn yourself and crumble to ashes

I cast Circle of Death

The enemies turn out to be disguised zombies with immunity to necrotic damage via magic rings.

I cast Mending

You forget how to cast mending

I cast Bardic Inspiration

You inspire your enemies to fight harder.

I cast Geas

You make a king fall to his death at the edge of a cliff and you are executed

I cast Disguise Self

You disguise successfully and learn your party-mates prefer you disguised.

I cast Dancing Lights

 But the lights flash violently in front of your eyes

I cast Tidal Wave

Your target grabs a surfboard and shreds the waves before coming at you. 

I cast False Life

you cast the spell, then realizing you forgot the material component, you take 1d4+4 necrotic damage

I cast minor illusion

You're not an artist and so the illusion looks more like a Picasso than anything realistic.

I cast Invisibility

 You cast the spell, immediately lose concentration, then realize your equipment was still invisible.

I cast counterspell

You counterspell your own counterspell.

I cast Melf's Massive Meteors aka Meteor Swarm.