Okay, the intransitive verb “lie-lay-lain” is one we often get wrong in the present tense. We say “I’m gonna go lay down,” when we mean “I’m gonna go lie down.” (note there’s no direct object.) “Lie,” the correct word, sounds okay even when we often say “lay.”
Ah, but the past tense of lie, which is “lay,” sounds wrong even when it’s correct! I think we’re just too used to something like a “-d” at the end of past tense verbs. Here’s a guy (Mike Peterson of Comic Strip of the Day for December 7, 2017) using it correctly. It’s the past tense:
He may not have been the worst of the lot, but he lay down with the dogs and now he’s getting up with the fleas.
Sorry, he’s right. It’s “lay.” “Laid” is wrong. I suppose Mike could have written, “…he laid his body down with the dogs…” That would be a little strange, but also grammatical.
The rule: “lay” is past tense of “lie.” Deal with it.