When one man is seen to be erect, or announces that he is so, it's signalling to others that he has found a sexual opportunity. This stimulates the erectile response in other men, in case they are able to join in. It's natural.
You'll probably become aroused again when you read of my afternoon, stripped naked, stroking and edging myself whilst wearing my cock and glans rings. Laid on my back, I finally came hands free simply by rocking my hips, thrusting my throbbing cock and nuts through thin air, and pushing and straining my engorged genitals until I forced myself to orgasm.
The penile constriction resulted in my cum being fired out in a strong jet, ropes spraying and matting my chest hair, pooling in my navel, and running off my sweaty torso and soaking into the bedsheets.
More men should experiment with rings. Find ones that are just right for you and it can feel fucking amazing.