suck out of one's thumb

Etymology
, from.

Verb

 * 1)  To make up, to fabricate, to pull out of one's ass.
 * 2) * 1956, Debates of the House of Assembly (Hansard), Vol. 90/91/92, page 2185.
 * "en"

- One cannot lay a charge, a charge which has simply been sucked out of one's thumb, and then say that the onus rests on the person against whom the charge has been made, to prove that it is not so.