Can I give my friend a puff of my asthma inhaler if he doesn't have asthma?

No. No one should ever give or take a medication that is not prescribed to them.
Is it necessary? Asthma inhalors are generally safe with minimum side effects. If it is accidentally inhaled by a healthy young person, the chances are he/she will be ok. They may be more harmful in peole with heart diseases, or glaucoma, depending on the person. The main question is whether the person needs an asthma inhalor. If yes, she/he should see a doctor.
No. No, you should not give anyone else your prescription medication. Only their doctor knows which type of medicine they need. All medicines have side effects and you may cause more harm than good by giving someone a medicine not prescribed specifically for them.
NO... Your asthma inhaler is prescribed by a doctor for you and it is not a medicine that should be given to anyone by a non-doctor. Your friend could develop symptoms like a rapid heart rate which could lead to heart rhythmn problems which could be life-threatening. Never share a prescribed medicine, including your inhalers, with anyone. If your friend wants an inhaler, he/she should see their doctor.