This is a British phase and is used in the past tense, it means that one beat-up another, however it is also used to descirbe a single yet dramatic hit.
"This chav was all up in Dean's face, so he twatted him, right between the eyes"
1. The act of a twat being masturbated 2. When a woman's vagina hangs down too low (similar to that of a waddle on a neck)
1. "I was so horny last night that I couldn't help myself! I had to twattle myself at work!"
2. "Did you see the photo of that girl on the Internet with the twattle? Her pussy lips hung down a good 6" from her body!"