How do I drop outgoing packets to specific host/port?
You could use the PF firewall:

Add this line to /etc/pf.conf to drop all packets to the given ip:port 

block drop out quick proto tcp  to 192.168.1.103 port 80


After changing pf.conf you should reload it with

sudo pfctl -f /etc/pf.conf


Eventually you will have to enable it with

sudo pfctl -e