由于

由 = 丨 + 曰 : Mnemonic symbol: 自由古巴， a cuba libre. The character 由 itself even looks like a cuba libre.

Maud Younger (y) is taking part in a charity auction in the outhouse's kitchen (ou2). She is auctioning the dinosaur bone (丨) next to her and is speaking into a microphone (曰). In the other hand she is holding a cuba libre (由), and she is already quite drunk.

于 = 亅 + 二 : Mnemonic symbol: prepositions (in, at, on, to, ...) are what glue the sentence together. Honey is as sticky as glue, so I'll represent 于 by a honey jar.

Yu the Great (于) was assigned to repair the electronics of the space station's kitchen (Ø2), but instead he was snacking honey from a honey jar (于). Unfortunately his capacitor (二) got stuck in the honey and now he has to use a crowbar (亅) to lever it out.