Green’s Dictionary of Slang

(US) snobbish, pleased with oneself.

1864		T.F. Upson n.d. in Winther With Sherman to the Sea (1958) 99: I must say I am getting all swelled up. We have a few boys who depend upon some to write and read thier [sic] letters. They mostly come to me now.
1905		R. Beach Pardners (1912) 64: Without being swelled on myself, I’ll say, too, that I once had more’n a local reputation in that line.
1918		A.N. Depew Gunner Depew 265: I was all swelled up about it, and I told the other fellows I had done the trick at last.
1925		G.H. Mullin Adventures of a Scholar Tramp 307: Whatever ye do, lad, don’t get swelled up on yerself.