関口やナベちゃんに「そんなとこ、ボッと立ってんなよ」と言われたことを思いだし、情けなさそうにうなずいた。
He recalled being told by 関口やナベ that ??? and bowed his head miserably.
To be honest, I'm stuck on everything in the quotes (something about blushing?) but, in particular I'm puzzled about the んな part in bold after the te-form verb. I'm guessing it's a contraction of たってのな but I've never seen that before either.