Thank you for reach8ng out to ask2.extension.

If you can dig them out, that would be the best way.  spot-spraying plants with a broad-leaf herbicide that's labeled for thistle control is an effective way to kill thistles.  You’d have to be careful not to spray plants you want to keep.  If you use an herbicide, be sure to follow label instructions.

On Thursday, May 9, 2024, 8:13 PM, Ask Extension <<personal data hidden>> wrote:

Good morning!   If you have an issue with breathing consider wearing a mask and definitely wear gloves.  All of the instructions for use will be on the package.  As long as you follow them, you should be fine.

Be sure to pick a non-windy day to apply the herbicide.

You can buy herbicides at any garden center, local hardware stores or any big box store.  Read the label to be sure that the herbicide is effective on thistles as some may not be.  

I would guess the neighbor had underlying issues.  Here is what I found for vinegar.  These are home remedies and results will vary.  They are not scientifically proven.  Be careful with these also, because they could change your soil.  It will likely take you 2 or 3 growing seasons to completely get rid them from your lawn.

Vineagar:    Cut the plant back to have an open wound.  Fill an empty spray bottle with vinegar. The vinegar needs to contain at least 20 percent acetic acid to be effective at killing weeds. No need to dilute as this makes it less efficient at killing weeds. Cut off at the base of the stem. Spray one to two sprays of vinegar directly on the cut of each thistle plant. The cut allows the vinegar to spread to the roots more quickly, which in turn kills the plant more quickly.

Saturating the unwanted plants once a week with this mixture helps control the problem. Do not spray the soil with vinegar. Sprinkle a pinch of salt at the base of each plant. Salt dehydrates the plants which make them die even faster. Too much salt will lower the quality of your soil, so use no more than a pinch of salt for each plant. After the plant withers and browns, removing it from the ground, roots and all, is a piece of cake.

LEMON juice acts similarly to vinegar when it comes to killing weeds. The high acidic level breaks down the composition of the plant, drying it out and preventing it from retaining moisture. This drying process works even faster on a hot, sunny day, so timing your weed control regimen to accommodate this will work to your advantage.

1/2 cup lemon juice 1-quart white distilled vinegar
Pour the two ingredients into a large empty spray bottle. If you don’t have a spray bottle large enough, mix the vinegar and lemon juice in a blender and pour the contents into your spray bottle as needed.

Good luck.