Runt of the litter informal
The smallest and weakest member of a group of animals born to the same mother at the same time.
The flock of birds neglected the runts of the litter.
Because it is smaller and weaker than others, a runt in a litter faces obvious disadvantages for survival.
In the wild, runts in the litter are less likely to survive.
A person who is completely unknown or has no connection with you
The guy I talked to at the prom last night is a perfect stranger.