drop in someone's lap - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Give to someone suddenly or without warning. What is given may be desirable, as in I'm just going to drop the promotion in her lap this afternoon, or it may be burdensome, as in They simply dropped the employment problem in our laps. The former usage dates from the mid-1500s, the latter from the mid-1900s.