When Richie and Eddie are in the booth with the lesbians, the glass that one of them was drinking out of disappears for one shot.
When Richie is pouring the oil over the food in the frying pan, he's holding the bottle in his right hand. In the next shot, where he sees the couple in the window, he's now holding the bottle in his left hand.
When Eddie and Richie come in from the pub, it's Friday night (Richie plans to cook a Friday night fry-up). Later, Richie moans about it being Saturday night. However, they went to the sex shop in broad day light, implying that at least one night had passed.
When Eddie clamps the pliers onto Richie's nose, if you watch carefully you can see the pliers bend a couple of times, showing that they are made of rubber or something similar.