hypokalemia caused by 4 D:
1-diarrhea
2-diabetes mellitus ...( insulin therapy )
3-digitalis
4-diuretics
good luck
thanks for sharing! I got some additionale information which one could include into you mnemonic (resource is master the bords third edition from Kaplan page 509), please feel free to comment

diarrhea and GI losses
diseases with increased aldosterone (e.g. Conn syndrome, Cushing syndrome, Licorice, disease of loop of Henle (Bartter syndrome))
drugs: diuretics, ß agonists (stimulate Na-K ATPase), insulin therapy, digitalis
decreased pH (alkalosis)
distal and proximal RTA
decreased intake (very rare)