I wrote the address in my best handwriting.

Danke erstmal. Deine Lösung klingt mir sehr ernst, oder täusche ich mich?
Es ist etwas scherzhaft gemeint, bzw. etwas übertrieben. Gibt es etwas, das in diese Richtung geht?

My very best (fancy) handwriting, perhaps. But even what Nancy suggested is more usual for a child to say than an adult, so if an adult said it you could certainly understand it as a little joke.

..in my very best handwriting... or even
..im my bestest handwriting...
makes me think of a little kid trying their hardest to write it very neatly :-)

Please note that 'bestest' is NOT the correct superlative form!
(good - better - best)

Thanks a lot!!!