Always wave, Its nice to acknowledge those who are courteous towards you and give way even if they might not need to.
Ive had some tw@ts on more than one occasion expecting me to slam into the back of a stationary bus or another stationary vehicle because they were in such a hurry to get to the next set of traffic lights they refused to slow down even for a second to leave me a small gap to scoot around the stationary vehicle which hardly takes a lifetime. Some people just feel the need to ruin other people's day