Why did the chief butler see fit to begin with the words, "Es Chata'ai Ani Mazkir ha'Yom"?
Seforno, Ohr ha'Chayim: So as not to convey the impression that he was complaining to Pharaoh for having incarcerated him.
The butler was speaking to Pharaoh. It should say 'El Pharaoh' and (in 41:10) "Avadecha.' Why does it say "Es Pharaoh" and "Avadav"?
Moshav Zekenim: He was speaking in front of Pharaoh and those around Pharaoh, and also Pharaoh listened.
Ohr ha'Chayim: Perhaps he spoke to Chachamei Mitzrayim, and asked them to speak to Pharaoh.
Ha'amek Davar: It is as if he was complaining about himself, for not mentioning Yosef to Pharaoh until today, in front of Pharaoh.
Why did he say "Chata'ai" (plural)? His only sin was letting a fly get into the wine!
Riva #1: He also sinned through not spilling out the wine.
Riva #2, Moshav Zekenim, Ohr ha'Chayim #1: His second sin was forgetting to mention Yosef.
Oznayim la'Torah: There are various opinions as to what their sin was - refer to 40:1:2:1 and 40:1:2:2 - and it may well be that both opinions are correct. 1
Targum Onkelos and Targum Yonasan both translate it in the singular. 2
Ohr ha'Chayim: In my eyes, it is like many sins.