That red filter means that Sim is very angry with your Sim and
may even get into a physical fight and/or try to bully your Sim!
Did you cheat on that Sim with another Sim by flirting, kissing, or
woohooing? That is most likely what caused it if it happened
suddenly! Or maybe that Sim was in love with the Sim that your Sim
married and is angry with you for taking his or her love muffin. If
it gradually appeared there, then your Sim was picking on and
bullying that Sim until he or she got angry with your Sim.