shoulder to shoulder, side-by-side, shoulder-to-shoulder
Mnemonic
[bi-] Bigfoot is in the [4] bathroom of the [-(e)ng] English manor taking a sauna. Suddenly two aristocratic 並 conjoined twins come in, literally 並 side by side. Bigfoot is not sure who is more strange, him or the 並 conjoined twins. I guess it is hard to compare them 並 side by side like that.