She tell me that my head bigger than a bus wheel
The girl he’s with is teasing him about the size of his head (which could have multiple meanings in itself), bus wheels are pretty big.
It could have three meanings, one obviously the size of his actual head, second being that he has a “Big Head” meaning he has a big ego or is very self-confident, or she could be talking about the size of his penis. All fit well into the next line.
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