Colloquial imperative (short for 覚えておけ/覚えていろ) meaning “Just you wait” or “I'll get you for this,” often used as a threat or angry warning; can be joking among friends but is strong in serious contexts.
そんなことをしたら、覚えてろよ！
If you do something like that, I'll remember it!/Just you wait!
（冗談で）また負けたら覚えてろよね、今度は本気で勝つから。
(Joking) If you beat me again, just you wait — I'll be serious next time.
彼は真剣な顔で『覚えてろ』と言って立ち去った。
He said 'I'll remember that' with a serious face and walked away.