When people lowball you and try to haggle down the price why do they laugh in your face when you tell them I'm sorry that's too low for me.

I am selling a bunch of Funko pops on Facebook Marketplace that I no longer need brand new never taken out of the package for $5 each. Some guy comes on and messages me and wants to do $40 for all 14 of them. I tell the person I'm sorry but that's too low and they immediately proceed to type LOL. With no other response just that. So I'm sitting here wondering what is so funny about that I truly don't get it? Also how do you feel about people that lowball you and try to haggle down the price to an unreasonable amount almost to the point where they're trying to rip you off?