IL, 25, known it my whole life and use it pretty regularly. “Lump it” = “Deal with it”
That said, the only other person I know who says it with any regularity is my mother…
Way to make me look bad. 
Mid-30s, Chicago. Either never heard it or never noticed it.
Glad to be of service!
Heard it from my mom (can’t remember if dad used it) when I was little. I’m 49 now and I’m not sure if I’ve ever heard it since then. Born and raised near Baltimore. Mom was born in '29.
This has got to be one of the most widespread “have you heard this expression” expressions ever. It’s all over the English speaking world and it crosses generation. I wonder where it came from and what’s with the lump?
This UK site, The Phrase Finder, says lump’s meaning ‘to look sulky or disagreeable’ figures in it. You have two choices-- like it or look disagreeable about it. I’ve never heard the word ‘lump’ used that way.
In Word Origins’ forum says “lump it” is an Americanism that replaced “stick it up your arse” in the phrase “Like it or _______.” Dickens picked it up.
Which makes me wonder how in the hell I’ve gotten through almost 37 years, living with a good cross section of people in different parts of the world, and have never heard it. I mean, I believe it’s common; I’m just always amazed when something 99% of people have heard somehow slips by me.