Texting etiquette is fairly simple to learn: don’t send paragraphs when you can send a sentence, emoji are like spices – use them sparingly – and never, under any circumstance, end a message with a full stop.
Like responding to a text message with “k” ; Ending a message with a full stop, unless deliberately signaling anger, is a HUGE mistake. One of the reasons is because it is often associated with anger and looks like the written equivalent of walking out on a conversation.
Apparently it’s down to something called ‘situational code-switching’, noted by linguistJohn J. Gumperz.
Given the frequency and informal nature of texting, a full stop comes across as formal and out of context.