The hand of a mage wiggles it's fingers, casting a harmful spell at you.  

I cast haste

You get so hasty, you go on an adventure but forget your pocket hankerchief.

I cast Slow.

You create an area in which all the time passes by so slow to not allow you do whatever you want at a fair speed.

I cast Blink

You blink perpetually and rapidly, hurting your eyes and rendering you unable to see.

Quote from Dertinus >>

You create an area in which all the time passes by so slow to not allow you do whatever you want at a fair speed.

I cast Blink

 You accidentaly blink into the nine hells instead of the ethereal plane and are obliterated by Asmodeus.

I cast Melf's minute meteors

You cast the spell and they appear over there... wait no, where'd I put them? I could've sworn they were over there! (Unfortunately they're so minute you lose them.)

I cast Enlarge/Reduce

You reduce yourself, letting my pet winged snake beat you up.

I cast find familiar

You find something that seems very familiar, but you can't quite remember what it reminds you of. How irritating!

I cast Guards And Wards

You summon 7d8 guard that are all surrounded with magical wards.  The magical wards give each guard 500 temporary hit points, Magic Resistance, resistance to physical damage, and +2 to AC and saving throws.  Also, each guard has a glyph of warding on it's chest that stores a spell of the DM's choice cast at 5th-level.  The glyph activates when the guard takes damage.  

Note:  the guards are hostile to ALL creatures that come close enough to it, including you.  They spawn within 30 feet of you.  

I cast moonbeam

The moonbeam’s ray reflects off of a mirror, and you being a changeling Druid, are instantly affected.

I cast Time Stop

You manage to stop time, but the accelerator got broken and now you can't start it again. 

I cast Dancing Lights. 

You are mesmerized by the lights.

I cast Wish

Quote from Drag0nb0rn >>

You are mesmerized by the lights.

I cast Wish

 Wish is an ambigous spell.  You need to specify what you are wishing for.  

I guess I'll just continue with a new spell.  

I cast pass without trace

It's so effective that not even you know where you are and thusly thou doth enter the void. 

I cast Speak with Animals

The words you seem to be speaking are percieved differently by the animals you are talking to.  The animals think you are cussing at them, and get angry and attack you.

I cast bestow curse (please don't just make the spell target me; that's boring)

Quote from EnchantedNinja12345 >>

I cast bestow curse (please don't just make the spell target me; that's boring)

 The spell targets you!

This is particularly bad as the DM has a homebrew spell made for the encounter that causes a doppleganger to appear and the curse, not being able to differentiate between the two of you, causes you have disadvantage while attacking the doppleganger. Conversely the doppleganger also has disadvantage on you, leading to missed attack after missed attack after missed attack. Three hours of combat go by before you finally land a hit on each other. Your party-mates, bored from the monotony of the encounter decide to head home. This leaves extra food left over that isn't able to be consumed, leading to the development of mold which soon overtakes the home. The extent of the mold is so bad that the home is condemned and you are forced to live on the streets for a while while searching for a new domicile.

I cast Acid Arrow

"Why would you put acid on my arrow?!" screams the ranger whose arrow just got melted. She seizes her sword and stabs you to death in revenge.

I cast Raise Dead. 

It turns out the person raised from the dead was executed under orders of the king and by raising them from the dead your party has become outlaws to be hunted down by all the realm's forces. Then the raised person steals your goods and makes off in the night.

I cast Sacred Flame

A planetar appears upon you and smites one of your allies with a beam of holy light.  Apparently, your "ally" has sinned and tortured an innocent barkeeper.  

I cast fire shield