Green’s Dictionary of Slang

dill-hole n.

[? SE dildo]

(US teen) the urethra; thus used as an insult.

[US]Da Bomb Summer Supplement 5: Dillhole (n.) A jerk.
OnLine Dict. of Playground Sl. 🌐 dill-hole n. (1) male urethra, hole in penis (2) insult (i.e. calling someone a prick).