The תוכחה.

 מנהגי קריאת תוכחה

There is a Minhag*, not to stand facing the בעל קריאה 
(in front of the בימה) while he Leins (reads)  the תוכחה.

*Another Minhag is that the עולה before the תוכחה leaves
the בימה immediately after his Aliya and doesn't wait for the
end of the next Aliya to do so.

The original Minhag, and in some Shuls even today,
when the Gabai wants to give an Aliyah to the בעל קריאה
he doesn't call him up by saying יעמוד פלוני ב"פ since he
is already standing there.
All he does is point at him to take the next Aliya.

Hence this is how the Minhag started for the בעל קריאה
to get the תוכחה since there is no need to call him up.

**The original Minhag was to put it in the contract  that
the שמש needs to take the Aliya of the תוכחה.

The רמ"א writes to call up יעמוד מי שירצה (no name) Whoever
is willing to take this Aliya.

There was a minhag*** to make a special מי שברך for the עולה.
It said all the קללות should turn into ברכות for the עולה.

The מקור חיים writes that the מי שירצה is a חיוב to be עולה
on the first day Rosh Hashana and on the first day Shavuos.
ie:  The מי שירצה is being compensated by getting an Aliya
on the first Yom Tov after the תוכחה 



*אגרא דפרקא,דרכי תשובה,מנחת אלעזר    
** מהרי"ל
*** מנהג פרעסבורג