I'm not going to accuse you of using. If you were using we'd see repeated evidence.

My first instinct would be to grasp your arm and press with my thumb while looking you in the eye for your reaction to the sensation. TBH, that'd be my compulsion is that was on my arm, too (minus the eye-looking part).

Good on you for donating plasma! Don't let any smooth-brain or pervert detract from that.