The most common and most likely answer to this crossword clue is the 6 letter word MISTER
I've seen this crossword clue in The Sunday Telegraph
M
I
S
T
E
R
More clues leading to the result MISTER
- Aerosol merits getting sprayed
- Scrooge catching Cratchitt’s latest name for him
- Film the Queen for him
- What do you call a guy who sprays plants?
- Sprayer‘s title?
- Chap that keeps house plants a little moist
- Man that’s useful with houseplants
- Scrooge investing capital in theory — that’s how he’s known
- Perhaps Scrooge swallows the first B
- Title thus originally adopted by Scrooge
Buddy explains!

The straight part
We know that "that’s what you’d call him" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that’s what you’d call him = mister.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MISTER mean?
MISTER noun- A title conferred on an adult male, usually when the name is unknown. Also used as a term of address, often by a parent to a young child.
- To address by the title of "mister".
- Someone's business or function; an occupation, employment, trade.
- A kind, type of.
- Need (of something).
- Necessity; the necessary time.
- To be necessary; to matter.
- A device that makes or sprays mist.