You are so annoyed or frustrated because you keep telling someone "no." that you don't feel like responding with a period and waste a fragment of a second, because they aren't worth it.
You have had to say "No." multiple times in response to a text so you you use no (without a punctuation mark) to show how annoyed you are
Them{wanna come over?}
You{No.}
T{Please?}
Y{"No." I said!}
T{pleeeeeeease???}
Y{No}
