The It's Always Sunny in Philadelphia star stated that he found a scene in which he was required to pretend to be drugged while allowing Jennifer Aniston to straddle him to be particularly difficult to shoot, according to the Los Angeles Times.
"It was awkward," Day said of the scene in question. "Actors put ourselves in awkward positions all the time. There's something methodical about it. You stand on a piece of green tape and say a line or you stand on a piece of green tape and pretend you're passed out while someone's half-naked on top of you. If you can't pull that off, God help you."
In Horrible Bosses, Day plays an engaged dental hygienist who has to fend off the sexual advances of Aniston's Dr Julia.
Day went on to confess that he feels no pressure to be extremely attractive in Hollywood.
"Knowing that I'm not a model and I'm never going to be has relieved me of the pressure of looking good," Day said. "If you don't establish yourself as McDreamy then you don't have to live up to it."
Aniston recently shot down rumours that she is topless in Horrible Bosses, stating that she had no idea where such a rumour originated.
In June, the actress revealed that she is very happy with her personal life.
Horrible Bosses opens in the US on July 8 and in the UK on July 22.
Watch the trailer for Horrible Bosses below: