Benoit is a French name pronounced like Ben Wa. When Benoit tells his name to Archer, he laughs because it reminds him of Ben Wa Balls, a sex toy.
As the Gran Prix was going on, Benoit checked Malory Archer, Sterling Archer, Lana Kane, and Ray Gillette into a nearby hotel. When Archer asks him his name, Benoit tells him his name, only for Archer to laugh, since it reminds him of Ben Wa Balls, a sex toy.
From Urban Dictionary
Archer: Sounds like 'Ben Wa Balls,' Benoit... Balls. See? You can't even say it without saying 'Balls.'
Archer: Hang on! Benoit Balls!