别相信虚情假意的狗

'Don't Trust False Dogs' suggests an unwillingness to believe in those who express insincere feelings or intentions. The dog here doesn't mean the pet literally but metaphorically refers to those people. There's a certain cynicism or wariness toward the ulterior motives of others. Maybe the user had encountered false friendship before and got lessons from it, so he or she would not fall into the same pitfall again.