The act of masturbating in semi-erect mode and never reaching climax because one cannot decide upon a particular wank model. Also occurs if a series of past sexual images is constantly infiltrated by erotic memories best forgotten (i.e. gay experiments, big fat old birds, your best mate's ugly mum, etc.). May be linked to anxiety.
I was really in the mood for a wank the other night but when I got to the outdoor privvy I had a wank blackout.