How much impact can the front bumper take without damage or causing it to loosen?
I park my TL in front of my house and in front of me is a very big spot. My neighbor still somehow backs up into my TL. There is never a car parked in front of my neighbors spot.

 

At least 5 MPH, but depending on the equipment and alignment of the two cars, cosmetic damage is likely at any speed.

 

Since it's parallel parking it seems like the front plate took the hit. I just checked my bumper and I didn't see any damage.
Is it possible for any hidden damage? It didn't seem like it was hit hard. Maybe just a little parallel parking tap.

 

I pull into my garage slowly everyday and tap a wooden/cloth folding chair hanging on the garage wall to tell when I'm all the way in. I've even come in faster (by accident, wasn't paying attention) at probably 5 or a little faster without any problems. Hope the info helps.

 

I have one of these electronic sensors that has a Stoplight display - Green when I enter, goes to yellow, then Red when I am in the programmed position. Love it.

A cheap solution is to suspend a tennis ball by string or fishing line from the ceiling at the point where you want the nose to stop.

 

The tennis ball trick works great in the garage! Now if I could only get my wife to stop parking so close to my TL, I can't even get in sometimes.

 

Thanks GaleForce.