I'm familiar with the expression "kannst du knicken" to mean "forget it", but can "Ich habe es geknickt" be used to express the idea of deciding against something (in the past tense)?
Yes, you can. At least: I did and do so and I get my message delivered.
So the infinitive of the verb would be "etwas knicken". Thus the usual rules for "knicken" apply "in general". Just with the addition that it is combined with "haben" instead of "sein". And that "etwas/es" is always present gramatically - and still get usually (visually) ommitted in colloqiual speech: Das habe ich geknickt. = Hab' ich geknickt.
I found this quote in a forum from round about 2013:
- (quote made by E. W.)
Post by C. S.:
Post by E. W.:
Variante 2, nebenbei eine weisse Konblauchsauce herstellen und die Mupfeln nach dem Kochen abgiessen und darin versenken.
Ich finde das würde den feinen Geschmack von den Muscheln völlig tot schlagen, Ede.
Ich gebe Dir Recht.
Ich habe es geknickt.
In this forum discussion, person E. W. proposes something about cooking. C.S. speaks against about it. And later E. W. confirms that the decision made was against own proposal. While there is no causal determination that E. W. talked about a past or present decision, I take it from the time stamps that there is actual doing in the kitchen involved.
While I personally would use "Hab' ich geknickt." to talk in a colloquial manner, your proposal is just fine. Instead of saying that someone else should "not think about it happening" it says that I decided to "not make it happen".
I guess it is due to "colloqiual" that I did not find a more "reputable" source.