How can you tell what a person's intentions approaching you are ?

If they look angry, turn and walk the other way and run if needed.
If they have a weapon, run.
If they are smiling, you're probably safe.
If they are smiling with a weapon, run faster.

Hope my advice helps

P.S. Can you give an example, i might be able to provide better info

 

Umm let me see if I get it correct.

You are 21 years old Pakistani lady with a boyfriend. There is a 28 years old janitor/building maintenance guy who is coming on to you. Both you and your boyfriend think his only intention is sex...

No need to chase his intentions if both you and your boyfriend sense he is after sex... assuming this is something you don't want, Ignore him. I had my share of leecherous men and best way is ignoring them and avoiding any situations that would leave you alone with them.

 

You can really only tell through experience with social interactions.

 

You can't tell for sure, but various cues in body language and speech can be used.

 

Hmm then you don't have to be within close proximity with this guy right? Stay away from him is the only think I can say to you if he makes you this uncomfortable.

On your question, there can be millions of reasons why a person can approach to another but you never know unless you ask them or let them get closer and share things.

 

Going with my intuition has never failed me. When ever I've gotten a bad vibe about a person, it has been for a reason and very accurate. It's pretty rare that people will give me bad vibes, though. When people, who I don't know, approach me out of the blue, sometimes I will panic internally. It's unexpected and I never quite know what they want until they ask. So far, it hasn't been anything bad.