As common as oral sex is, some guys take Cock Worship to whole different level which I feel makes it a fetish. It's hard to explain the fine line that defines it. Some are simply obsessed with it and it's all they want or only way they get off.
Once a long time ago I picked up a hot young cute very masculine English guy, who was visiting for a week in San Francisco. He was into watching straight porn while he sucked cock and swallowed cum. That was ALL he like and all he wanted. Suck cock and swallow load after load and he didn't seem too very selective about who it was either as long as the guy had a cock and shot a decent load. He spend day and night of that week on his knees at the bookstores with gloryholes and at the Windmills in Golden Gate park at night. I'd say that guy has a Oral Cock Fetish and he wasn't just another cocksucker either!