Interestingly the lump in this phrase is apparently unconnected with lump meaning bump or protuberance. OED gives the following etymology:
[Of symbolic sound; cf. dump, glump, grump, hump, mump.]
The oldest sense was to look sulky or disagreeable and, as OED tells us, “In early quots. always in collocation with lour.”
1577 STANYHURST Descr. Irel. in Holinshed Chron. (1807-8) VI. 5 They stand lumping and lowring..for that they imagine that their evill lucke proceedeth of him. 1581 RICH Farewell Ddivb, She beganne to froune, lumpe, and lowre at her housebande. 1593 Tell-Troth’s N.Y. Gift 19 At home they will lumpe and lower. 1594 LODGE Wounds Civ. W. IV. i. F2, How fare these Lords that lumping pouting proud Imagine how to quell me with their lookes? 1847 HALLIWELL, Lump..(3) To be or look sulky. Devon.
The modern usage has a first cite of 1833.
2. trans. In antithesis with like: To be displeased at (something that must be endured). colloq.
1833 NEAL Down Easters I. vii. 104 Let ‘em lump it if they don’t like it. 1835-40 HALIBURTON Clockm. Pref. (1862) 6 A man that would be guilty of such an action is no gentleman, that’s flat, and if you don’t like it you may lump it. 1878 MRS. STOWE Poganuc P. xi. 94, I’ll buy clothes as I see fit, and if anybody don’t like it, why they may lump it, that’s all. 1893 GRANT ALLEN in R. Blathwayt’s Interviews Pref. 11 Whether we like him or lump him, he [the Interviewer] is master of the situation.
BTW is this phrase used in the States?
No connection at all to anything written above, just adding this because I’m so pleased. Just watched the 1947 movie, It’s A Joke, Son! featuring Kenny Delmar playing a character called Senator Beauregard Claghorn. And would you believe, I say would you believe, that this is the very character which inspired the immortal Foghorn Leghorn? It’s a delight to watch, like seeing the old rooster take human form. (And as an added bonus the wonderful Una Merkel is in it!)
NB I see Foghorn Leghorn’s first appearance was in 1946, a year before this movie, which puzzled me until I checked and found that Senator Claghorn had been a long-running character on the popular Fred Allen radio show for years previously to the movie.