Learn Hardcore Turkish: Lütfen bir daha böyle geç kalma. - Please don't be late like this again.

The subject is sen (you, singular/informal). Turkish usually drops subject pronouns unless you want emphasis. You can say Sen lütfen bir daha böyle geç kalma to stress that it’s you specifically.

How do I say this formally or to more than one person?

Use the plural/formal imperative:

Lütfen bir daha böyle geç kalmayın. (neutral polite/formal)
Lütfen bir daha böyle geç kalmayınız. (very formal/polite) Form: kal- + -ma (neg) + -y- (buffer) + -ın/ınız (2pl imperative).

Why is it geç kalmak and not something like geç olmak or geç gelmek?

geç kalmak is the set expression for “to be late.”
geç gelmek means “to arrive late,” focusing on the act of coming late.
geç olmak is not used to mean “be late.” In many contexts geç kalmak is the most natural choice.

What exactly does bir daha mean here?

Literally “one more (time),” it means “again,” and with a negative it often carries the sense of “ever again.” Compare:

Bir daha yapma = Don’t do it again (ever).
Tekrar/yeniden yapma = Don’t do it again (more neutral/technical).

What does böyle add to the meaning?

böyle = “like this/in this way.” It narrows the prohibition: “don’t be late like this (to this extent/in this manner) again.” Without it (Lütfen bir daha geç kalma) it’s a general “don’t be late again.”

Is the word order bir daha böyle fixed? Can I move these around?

Typical and most natural is to place adverbs before the verb, with time/frequency (bir daha) before manner (böyle):

Lütfen bir daha böyle geç kalma. (most natural)
You can front böyle for emphasis:
Böyle bir daha geç kalma. (puts focus on “like this”)
Avoid splitting them oddly (e.g., Lütfen böyle bir daha geç kalma) as it can sound awkward.

Can I move lütfen to a different place?

Yes. Common placements:

Lütfen bir daha böyle geç kalma. (standard)
Bir daha böyle geç kalma lütfen. (softer, conversational)
Lütfen can also appear after the verb phrase, but keep the sentence clear and not overly long.

How can I make the warning stronger or more emphatic?

Use intensifiers:

Sakın bir daha böyle geç kalma! (Don’t you dare…)
Bir daha asla böyle geç kalma! (Never again…) Punctuation (exclamation mark) also adds force.

Should this end with a period or an exclamation mark?

Both are acceptable:

. = polite request tone.
! = firmer, more urgent tone. Choose based on how strong you want to sound.

Why is it -ma and not -me?

Vowel harmony. The last vowel of the stem kal- is a (a back vowel), so the negative suffix uses the back form -ma. With front vowels you’d use -me (e.g., gelme = don’t come).

Where does the buffer -y- appear, and why isn’t it here?

In 2sg negative imperative, there’s no person ending, so no buffer is needed: kal-ma.
When you add a vowel-initial ending (e.g., 2pl imperative -ın/-iniz), you need -y-: kal-ma-y-ın → kalmayın.

Could geç kalma be read as a noun like “being late”?

Yes, geç kalma can be a verbal noun (“being late”) in other contexts, e.g., Geç kalma alışkanlığı (the habit of being late). Here, with Lütfen and the imperative context, it’s clearly a command.

Are there natural alternatives that keep the same idea?

Yes:

Lütfen bir daha geç kalma. (no “like this” nuance)
Lütfen bir daha bu kadar geç kalma. (don’t be this late)
Bundan sonra lütfen geç kalma. (from now on, don’t be late)
Lütfen bir daha böyle geç gelme. (focuses on arriving late)