As the big bang theory is unlike other comedy sitcoms as this programme i wouldnt say its sexist per se. even though penny is nowhere near as smart as any male on the show she isnt really portrayed as a bimbo, like many other women on tv are. she also "beats" the really smart one (sheldon) a few times, like he gives her 3 strikes and kicks her out of their flat in one episode, they keep trying to get back at eachother and in the end she calls him pretending she is his mother and gets him to apologise.

she also seems quite open to learning whatever they're talking about, while most women on tv keep on being dumb. while you can easily say the show is sexist, you'd be better off watching a few episodes and going pretty far into what the situations/events represent.

she also tends to hold the power because all the guys are trying to impress her, do things to please her etc instead of the other way around like on normal tv show