I am paranoid about my car being parked parallel in the street. If someone taps their bumper to my bumper , will it ruin the structure of the car? Will it mess with my alignment? How bad is it to receive a love tap? Don't know much about cars, so sorry about this stupid question.
Not for the structure.
Industry regulations require that:
a car's safety systems must still function normally after a straight-on pendulum or moving-barrier impact of 4 km/h (2.5 mph) to the front and the rear
On modern cars, the bumper you see is a thin plastic cover. Underneath that cover is a large piece of foam or other absorbent/elastic material. Behind that foam is the actual metal structure of the vehicle. The foam looks like this, and it is this foam that occupies most of the space/shape in the bumper:
A low speed impact compresses the foam, then the foam springs back to its original shape thus retaining its ability to cushion the next impact.
While the structure and safety equipment of your car is meant to survive love taps unscathed, mechanical components and paint aren't designed to the same standard. For example, in an automatic transmission there is a pin that engages when the transmission is placed in Park. Bumping the car, especially repeatedly, can't be good for this pin and eventually the pin may break, requiring transmission repair or replacement . If you are concerned with being love tapped, manually setting the parking brake can be a good idea . And any sort of contact with the bumpers is likely to scratch/scuff them, even tear if the contact is with a license plate frame at an angle.
: For the pin to break the car would need to be tapped either many many times or be hit relatively hard. In any event setting the parking brake will likely extend the life of transmission.
: One downside to setting the parking brake is the brake pads/shoes can get stuck to rotors after rain/snow, especially in winter. I usually do set the parking brake but I don't pull it all the way up as high as it will go.
Structure wise you shouldn't worry about it. Bumpers are made to take a 5mph hit with zero damage (supposed to be here in the States, anyway). You'll see superficial damage to the paint and outer structures, though ... besides a scuff, a torn bumper cover may come of it.
In the good old days of parallel curb parking , more than a few people backed until they "touched" the car behind , then went forward until the touched the car in front . Everything was good unless there was broken glass from lights.