Short for Diphenhydramine
(trade name Benadryl), an over-the-counter antihistamine and sedative. Recreationally used for its deliriant effects, often producing visual and auditory hallucinations indistinguishable from reality. Side effects are consistent with tropane glycoalkaloidal poisoning and death at high overdosage.
Yo man I popped 20 Diph's last night and I could have sworn my house was on fire.