Only bikes that ever gave me problems:
Enfield Bullet 350 which did not have the rubber coating on the kick starter any more. Only the nasty sharp edged "washer" that's supposed to hold it in place. I tried to start the bike wearing espandrillos (those biodegradable sisal & canvas "shoes") and shorts

Lost a bit of skin off my shin. Eina.
An SR500 which I had sold a few months earlier. Customer phones and says the bike won't start. After he confirmed he did try a new spark plug I pack my tools into the car and drive to the other end of Munich.
Kick three times. Nothing.
Put new plug in. Starts first kick.
Turns out he had tried ANOTHER plug. Another old, dead one

A KTM 250 two smoker. Bike was plated and therefore had to get a roadworthy / TÜV every other year. The guy drops it off with me and explains that for the roadworthy he put the corked road legal zorst on but did not bother to change the carb jetting and the bike is therefore "a bit hesitant"

to start.
After checking and readying everything for the test I try top kick the damn thing for I don't know how long. Just when I consider phoning the customer to tell him to take the piece of junk through the test himself it starts.
Onto the bike & ride it through town (had to get to a tester I knew due to the "minor gearbox oil leak without imminent danger of oil dripping off" - it left puddles behind when parked

)
With the gross carb - zorst mismatch the thing was a totally unrideable bitch as the powerband was actually narrower than the gaps between the gears. I stalled it once when trying to pull away but got it runnnig just in time for the next robot phase.
Got to testing station, everything checked ok, now the dude tells me: "You start it for me, you know, kickstart? You're better at that"
About an hour and three buckets of sweat later the testing station closes and the tester agrees to store the bike overnight for the customer to start it the next day for the obligatory test run. He also promises to give me a lift back to the workshop.
I say: "F*** that thing, I'll try one more time! And it starts!!!
Tester on, around the block, swop riders, sticker onto number plate and I made it back to the shop without stalling

Kranke Teile Mattighofen. My leg still hurts from thinking about it

Andrew's KL600 before the rebore. A bitch turned a beaut after the well deserved and overdue rebuild gave the engine some much needed compression.
The BMW Airhead "Katapult" is a bit of a joke. Tried it once or twice on a R90 and decided it's best to keep the electric starter & battery in good nick. Interestingly the "Katapult" works just fine on the Ural probably due to lower displacement and compression.
Two things: DIR and make sure the bike is on good nick (which includes making fuel and sparks available to the engine)
Not scared of kick starters. I must admit I have an unfair advantage having started my two wheeled life on an SR500
