How can I kill whatever process is using port 8080 so that I can vagrant up?

Fast and quick solution:

lsof -n -i4TCP:8080

PID is the second field. Then, kill that process:

kill -9 PID

Less fast but permanent solution

1. Go to /usr/local/bin/ (Can use command+shift+g in finder)

2. Make a file named stop. Paste the below code in it:

#!/bin/bash
touch temp.text
lsof -n -i4TCP:$1 | awk '{print $2}' > temp.text
pidToStop=`(sed '2q;d' temp.text)`
> temp.text
if [[ -n $pidToStop ]]
then
kill -9 $pidToStop
echo "Congrates!! $1 is stopped."
else
echo "Sorry nothing running on above port"
fi
rm temp.text

3. Save this file.
4. Make the file executable chmod 755 stop
5. Now, go to terminal and write stop 8888 (or any port)

This might help

lsof -n -i4TCP:8080 

The PID is the second field in the output.

Or try:

lsof -i -P