mc5 - ... so help me God.

[BtD] When I worked in kennels, I made such a mess of things they told me to go take a long walk.

Then I joined an athletics club, but I was so terrible at the field events, they told me to go take a running jump.

Back in high school, I was on the cross-country team until I was given my walking papers.

None of the above were hilarious. I hate them all. They are not classic online Mornington Crescent.
I used to work in a glue factory, but I couldn't stick with it.

Tuj

On a similar line, I applied to be a lumberjack, but I just didn't cut it.

Zooological Keeper

I used to be a Spice Girl.

barbacoa

I used to be a drag queen, but I dropped out.

Tina

I worked in a spice factory, but couldn't cut the mustard.

Tina

I tried road paving once, but didn't make the grade.

Dunx

I used to drive a cement lorry, but gave it up because I wanted something more concrete.

DrQu+xum

I became a partner in a building firm, but the other guy screwed me over and bolted.

barbacoa

I worked in a fireworks factory, but the work fizzled out.

Zooological Keeper

I used to be a terrible songwriter until I composed myself.