There are various phrases and synonyms that can be used instead of "forget your lines". Some popular options include "go blank", "draw a blank", "lose your place", "mind goes blank", "memory lapse", "stage fright", "flub your lines", "fumble your words", and "stumble over lines". Each of these phrases can be used to describe a situation where someone forgets or struggles to remember the lines they are supposed to say, whether on stage, in a meeting, or during a presentation. Using these synonyms can help add variety and nuance to your language and convey different degrees of difficulty in remembering lines.