There is an area of Japanese that has a special place/knife in my heart:

Phrases that my useless brain spits out, even though I know they're wrong.

There are A LOT of these.

For example...

One Hand

This is one of my oldest bad habits in Japanese.

The correct word for "one hand" is 片手 (katate).

I always say ひとて (hitote) (<--NOT a word). I guess because sometimes ひと (hito) means "one," like in these words:

一つ (hitotsu; "one [thing]")
一人 (hitori; "one [person]")
一言 (hitokoto; "one comment; one sentence; one phrase.")

Here are some sentences, for you study nerds:

一つください。
hitotsu kudasai.
One (thing), please.
(Literally: "one [thing] + please.")
(Note: For example, when you're asking for one [something] at a store or food stand.)

一人で旅行行ってきた。
hitori de ryokou itte kita.
I went on a trip by myself.
(Literally: "alone + trip + go and + came.")
(Note: Adding a で to 一人, "one person," makes it "alone; by oneself.")

一言コメントお願いします。
hitokoto komento onegai shimasu.
Can you leave us a comment, please?
(Literally: "one sentence + comment + please.")
(Note: For example, a reporter might say this to someone.)

The reason we use 片, though (or the way I chose to remember it, at least), is that we are talking about one of two sides.

So it is preferable, for example, when talking about one of two body parts...

片手 (katate; one hand)
片足 (kataashi; one foot*)
片脚 (kataashi; one leg*)
片耳 (katamimi; one ear)
片目 (katame; one eye)

*Notice that for kata + ashi, the word is the same, but the kanji is different depending on if you're talking about "one foot," 片足, or "one leg," 片脚. I actually didn't know this until just now. So don't thank me--thank Rei for teaching me. ^_^

Sentences, please!

The cool thing about this is that BOTH hands/feet/legs/ears/eyes, will all use 両 (ryou) instead of 片 (kata):

両手 (ryoute; both hands)
両足 (ryouashi; both feet)
両脚 (ryouashi; both legs)
両耳 (ryoumimi; both ears)
両目 (ryoume; both eyes)

This is awesome, because we can use the following short convo to memorize all of these:

A:
両手とも痛いの？
ryoute to mo itai no?
Do both of your hands hurt?
(Literally: "both hands + とも + painful + の？")

B:
ううん、片手だけ。
uun, katate dake.
No, just one hand.
(Literally: "no + one hand + only.")

Lather, rinse, repeat:

A:
両手 [ 両足／両脚／両耳／両目 ]
とも
痛い
の？
ryoute [ ryouashi / ryouashi / ryoumimi / ryoume ]
to mo
itai
no?
Do both of your hands [ feet / legs / ears / eyes ] hurt?

B:
ううん、
片手 [ 片足／片脚／片耳／片目 ]
だけ。
uun,
katate [ kataashi / kataashi / katamimi / katame ]
dake.
No, just one hand [ foot / leg / ear / eye].

覚えとこう。
oboetokou.
Let's remember this/these.

(Note: We've seen this before [though I forget which lesson number]. The te-form of 覚える (oboeru; to memorize; to remember) is attaching to the volitional form of おく (oku; to place, to do something in advance), then it's getting abbreviated: 覚えておこう → 覚えとこう.)
(Note #2: You should remember this phrase as is. Then just say it when you come across something you want to remember. Like the names of sushi at a restaurant, for example.)

I'm home!

One of the first things you learn in Japanese textbooks is that when you leave your house, you say (to family members/roommates):

いってきます！
ittekimasu

Then they say:

いってらっしゃい！
itterasshai

When you get home, you announce yourself by saying:

ただいま！
tadaima!

And they welcome you back home by saying:

おかえり（なさい）
okaeri (nasai)

Like all studious beginners, I had that down no problem.

Then like three months ago I started mixing up ただいま and おかえり... like every day.

I think I'm losing my mind.

We've seen this common mistake before, too (Lesson #38), when the "only of scarcity," as I call it, is しか and NOT だけ.

That is, if you want to say "only" to emphasize that you have not done much of something, then use しか:

A:
ビールめっちゃ飲んでるね。
biiru meccha nonderu ne.
You're really knocking them back, aren't you? // You're drinking a lot of beer, huh?

Good B:
三つしか飲んでないよ。
mittsu shika nondenai yo.
I've only drank three!

Strange B:
三つだけ飲んだ。
mittsu dake nonda.
three + only + drank

Why do I keep mixing these up?

I recently came up with a new theory explaining this--muscle memory.

It always feels like my mouth is making these mistakes, not my brain.

I mean, I've said them so many times that it's like their stuck in my mouth muscles. So my new goal (starting 14 seconds ago) is to repeat the correct versions of these (out loud!) 43,212 times each... or just until I get bored and do something else.

Maybe that way I can retrain my muscles.

Bonus Phrases

覚えておこう。
おぼえて　おこう。
Let's remember this/these.