Historical! Romans saw sexual relations as a matter of 'penetrator' and 'penetrated', or 'active' and 'passive', or 'receiving pleasure' and 'giving pleasure'. In all of these cases, it was the second which was 'shameful' (to at least some degree), and the former which reflected virility and manliness.
In matters of oral sex, then, Romans held that receiving oral sex was manly - giving it was 'effeminate' or 'servile'. Some very odd sexual standards, the Romans.