What does "ねーし" mean? For example: 笑ってねーし！
～ねーし ＜＞ ～ねえし ＜＞ ～ないし
笑ってねーし would be a colloquial way of saying "I didn't laugh!" A more standard way of saying it would be 笑ってないし。
The elongation(ー) after ね means to elongate the sound of the previous letter (hence ねえ above). The ねー is the colloquial form of ない。 The し is another (normally colloquial) letter usually used to list things. In this instance however, its use is at the end of a rebuttal to an inquisition or accusation.
A: Why haven't you emailed Tom?
B: Because, I don't know his email address!
Similar colloquial words can be found in this similar question here.