A noun. Squidtardo affectionately refers to a dear friend prone to doing/saying things that are 'retarded' (in an endearing sense). The word also represents the subject's propensity to fail to accompany friends on outings when they really want he or she to do so. Therefore, they are also 'the suckiest thing in the world' - a squid.
You're not coming to dim sum and karaoke tonight 'cause you hurt your knee working at the supermarket? You are such a Squidtardo!