How about VSRA. Very short reply accepted. VSRE can come off a bit harsh both for the sender and receiver. By using VSRA you're saying "hey, if you're real busy I won't be offended by a super short response. As others have mentioned here, the idea of VSRE can be socially awkward. By making it optional you avoid that. I suggest this not as a replacement but as an alternative. You could use VSRE with people you know well and VSRA with anyone else.