When someone tells you to "lay it on," they are asking you to speak truthfully or candidly. There are a few synonyms for this phrase that could be used interchangeably depending on the situation. For example, you could say "give it to me straight," "speak your mind," or "shoot straight with me." All of these phrases convey a similar request for honesty and directness. Similarly, you could also use phrases like "tell me how it really is" or "don't sugarcoat it" to convey the same sentiment. Ultimately, the goal is to encourage open communication and an honest exchange of ideas or opinions.