便 (Kanji for convenient　/ poop)

This is pronounced BEN in poo-related words, and BIN in mail-related words.

Onyomi

BEN	BENny Hill had BEEN doing a TV show known for poop jokes. As well as boob jokes and other cultural fare.

A person poops when it is convenient, and then the next day they have to poop all over again.

たよ*り	news or communication from someone - a letter. A simple postcard now and again. Is that so much to ask? Mr. thinks-his-shit-don't-stink??? ★★☆☆☆

便利(べんり) な	handy, convenient ★★★★★ 便 (convenient　/ poop) + 利 (handy) = 便利 (handy, convenient)
不便(ふべん) な	inconvenient ★★★★☆ 不 (un) + 便 (convenient　/ poop) = 不便 (inconvenient)
郵便局(ゆうびんきょく)	post office ★★★☆☆ 郵 (mail) + 便 (convenient　/ poop) + 局 (department) = 郵便局 (post office)
排便(はいべん) する	defecate ☆☆☆☆☆ NP 排 (eliminate) + 便 (convenient　/ poop) = 排便 (defecate) the dook (doctor word, although it's sure to get a chuckle if you use it)
小便(しょうべん) する	the wee ☆☆☆☆☆ NP 小 (small size) + 便 (convenient　/ poop) = 小便 (the wee) the wee (Doctor's word)

"Hard" as a ROCK.

A person uses a BERET to keep his head warm,

but another person takes a poo in the RICE FIELD.

You're welcome.