Hi Jay, These are not sentences. A sentence contains a subject and its predicate (what is said about the subject). * Ask me to follow back: Block. (If you ask me to follow you, I will block you. /Ask me to follow you, and I will block you.) There is an implied condition here, and the consequence is expressed by a colon (:). * No response to DM (I won't respond to any direct messages.) The subject (I) is omitted here as the warning is directed at the reader instead. This way of writing is similar to "No Speeding" signs along highways where a warning has to be given very quickly by using as few words as possible. Imagine how odd it would be to see a grammatically correct sign that says: You must not speed! As you can see, our register varies according to the demands of the context, medium, audience and formality. Writing on social media is very informal, lengthy pleasantries are done away with and grammar rules could be sidelined. One reason could be a need to get messages across fast and with as few words as possible, so that we can grab our readers' attention. Lastly, to answer your question, they are not grammatically correct but they are acceptable and understandable in social media.

Technically, they are grammatically incorrect, but in the context of social media, they are understood as abbreviations and therefore acceptable. For example, "Ask me to follow back : Block" means "If you ask me to follow you back, I will block you." and "No response to DM" means "I do not respond to Direct Messages (so do not DM me)." Hope that helps!

In the context of social media, where writing tends to be more casual and lax in terms of grammar, then I would say yes, Those two sentences are sufficiently correct for social media. If you were to use those two sentences in an academic or professional paper, then no, they are not correct. I will provide a more formal translation below. 1: If you ask me to follow you back then I will block you. 2: I will not respond to direct messages.